Doctoral Thesis
Foot trajectory when crossing over irregularly shaped obstacles

Yuka Miura

Graduate School of Humanities and Social Sciences

Hiroshima University

March 2023

Foot trajectory when crossing over irregularly shaped obstacles

By Yuka Miura

A THESIS SUBMITTED IN PARTIAL
FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF

DOCTOR OF PHILOSOPHY
in
Graduate School of Humanities and Social Sciences(Integrated Arts and Human Sciences Program)

Hiroshima University

March 2023

Abstract
The risk of falling during obstacle crossing is assessed based on clearance,
which is the distance between the obstacle and the toe when the toe is directly above the
obstacle. The obstacles that are encountered daily have a wide variety of shapes.
However, most previous studies on walking over obstacles investigated simple shapeswith a single leaf height. In this study, the foot trajectory was evaluated when stepping
over irregularly shaped obstacles such as staircase-shaped (Experiment 1) and oblique(Experiment 2) obstacles.
Experiment 1: Sixteen healthy young adults performed obstacle-crossing tasks.
The obstacle was staircase-shaped, combined with a rectangular obstacle with a heightof 9.0 cm on the contralateral leg side and a rectangular obstacle with a height of 22.5
cm on the ipsilateral leg side. The results revealed that there was greater foot clearance
on the ipsilateral side when the obstacle on the contralateral side is higher than therectangular obstacle.
Experiment 2: Sixteen healthy young adults performed obstacle-crossing tasks.
The obstacles had trapezoidal and rectangular shapes when viewed from the frontal
plane. The results revealed that the foot control in the mediolateral direction was
adapted to the shape of the obstacle.
The foot trajectory of the lower limb in obstacle avoidance walking was not
only determined by the height of the obstacle directly under the foot but may also be
influenced by the shape of the opposite leg movement and the shape of the entire
obstacle.

Abstract (in Japanese)
障害物跨ぎ越し時の転倒リスクは、障害物とつま先の距離であるクリアランスによって評価される。日常生活における障害物は、様々な形状のものがあり得るが、障害物跨ぎ越し歩行を対象とした殆どの先行研究では、一様な高さを持つ単純な形状の障害物を用いて評価が行われてきた。そこで本研究では、階段状（Experiment 1）や斜め（Experiment 2）といった、不定形な障害物を跨ぐ際の足部軌跡の評価を行った。
Experiment 1：健常な若年成人 16 名を対象に、歩行中に右足、左足の直下の障害物の高さが 9.0 cm の長方形の障害物と右足直下の高さが 22.5 cm、左足直下の高さが 9.0 cm の階段状の障害物を跨ぐ課題を実施した。その結果、後続脚先行脚共に階段状の障害物を跨ぐ際のクリアランスは、長方形の障害物を跨ぐ際のクリアランスと比較して有意に大きくなり、反対脚が跨ぐ障害物の高さの影響を受けることが示された。
Experiment 2：健常な若年成人 16 名を対象に、歩行中に前額面から見て台形の障害物と長方形の障害物の 2 つの形状の障害物を跨ぐ課題を実施した。
その結果、障害物の形状に応じて左右方向の足部軌跡が制御されることが明らかとなった。
このことから、障害物跨ぎ越し歩行における下肢の足裏軌道は、足裏直下の障害物の高さによってのみ決定されるのではなく、反対脚の運動や障害
物全体の形状を考慮することによって制御される可能性があることがわかった。

Contents
Chapter 1. General Introduction ..............................................................................................1
Abstract ................................................................................................................................1
Abstract (in Japanese) ..........................................................................................................2
1.

Mobility is an indispensable ability for survival in animals ...............................................3

2.

Visual information is necessary for humans to perform adaptive walking .........................4

3.

Clearance depends on the energy consumed and the risk of contact with obstacles ............54.

Interaction of motor control of the lower limbs during walking over obstacles ..................65.

Obstacle shape affects the motor control of the lower limb during obstacle traversal .........86.

The hypothesis and objectives of this study ....................................................................10

Chapter 2. Review of the Literature ....................................................................................... 12
Abstract ..............................................................................................................................12
Abstract (in Japanese) ........................................................................................................13
1.

Summary......................................................................................................................142.

Adaptive locomotion .....................................................................................................14

3.

Obstacle crossing task...................................................................................................16

4.

Obstacle crossing task in VR and AR environments .......................................................18

5.

Research on obstacle crossing reflecting realistic and complex contexts .........................20

6.

The purpose statement of the research...........................................................................24

Chapter 3. Foot clearance when crossing obstacles of different heights with the lead and traillimbs (Experiment 1) ............................................................................................................. 26
Abstract ..............................................................................................................................26
Abstract (in Japanese) ........................................................................................................27
Introduction........................................................................................................................28
Methods ..............................................................................................................................30
Participants.....................................................................................................................30
Experimental protocol.....................................................................................................31
Data collection.................................................................................................................32
Data analysis ...................................................................................................................33
Statistics..........................................................................................................................34
Results ................................................................................................................................35
Discussion ...........................................................................................................................41
Conclusions.........................................................................................................................45
Funding ..............................................................................................................................46
Chapter 4. The shape of the obstacle affects the left-right trajectory of the lower limb when
stepping over the obstacle (Experiment 2) ............................................................................. 47

Abstract ..............................................................................................................................47
Abstract (in Japanese) ........................................................................................................48
Introduction........................................................................................................................49
Methods ..............................................................................................................................52
Participants.....................................................................................................................52
Experimental protocol.....................................................................................................53
Data collection.................................................................................................................56
Data analysis ...................................................................................................................57
Statistics..........................................................................................................................58
Results ................................................................................................................................58
Discussion ...........................................................................................................................63
Conclusions.........................................................................................................................68
Funding ..............................................................................................................................69
Chapter 5. General Discussion................................................................................................ 70
Abstract ..............................................................................................................................70
Abstract (in Japanese) ........................................................................................................71
1.

Objectives and results of this study ................................................................................72

2.

Explanation of similarities and differences between Chapters 3 and 4 ............................73

3.

Contribution to the field of gait control..........................................................................74

4.

Solving the fall problem ................................................................................................80

5.

Limitations ...................................................................................................................82

Reference ............................................................................................................................... 84
Acknowledgments ................................................................................................................ 103

Chapter 1.
General Introduction
Abstract
Locomotion is an essential ability for the survival of animals. They use various
means of locomotion, of which walking is the most common form performed bymammals. Among mammals, humans are the only animals that habitually engage inbipedal locomotion, and walking is the main means of locomotion for humans. Human
gait is often adapted depending on the environment, even when the environment is newor unpredictable. To perform such adaptive walking locomotion, visual information isnecessary. To safely perform a particular type of adaptive gait, i.e., traversing obstacles,
it is necessary to instantly determine the shape and position of obstacles that appear in awalking path based on visual information, and control the lower limbs according to theshape of the obstacle to be crossed. The results of previous studies on the traversal of
obstacles suggest that the foot trajectory depends on the shape of the obstacle, considering
the trade-off between minimizing energy cost and the risk of contact with the obstacle, as
well as the motion of the opposite limb.
Based on these findings, it is hypothesized that the foot trajectory can becontrolled in vertical and lateral directions by considering the height of the obstacle
traversed by the opposing leg, the motion of the opposing leg, and the shape of the
obstacle. The objective of this study was to determine whether the foot trajectory during
obstacle crossing is influenced by the shape of the obstacle.

1Chapter 1.
General Introduction
Abstract (in Japanese)
動物の生存には移動能力が必要不可欠である。哺乳類は様々な移動手
段を用いているが、その中でも歩行は最も一般的な移動手段である。哺乳類の中で常習的直立二足歩行をするのはヒトだけであり、歩行はヒトの主な移動手段である。ヒトの歩行は、新しい環境や予測不可能な環境であっても、環境に応じて適応的に変化することができる。このような適応的な歩行運動を行うためには、視覚情報が必要である。適応歩行の一つである障害物跨ぎ越し歩行を安全に行うためには、歩行経路に現れる障害物の形状や位置を視覚情報に基づいて瞬時に判断し、跨ぐ障害物の形状に応じて下肢を制御する必要がある。障害物横断に関する先行研究の結果から、障害物の形状に応じて、エネルギーコ
ストの最小化と障害物との接触リスクのトレードオフを考慮し、反対側の四肢の運動を考慮した足運びを行うことが示唆されている。
これらの知見に基づき、対向脚が通過する障害物の高さ、対向脚の運動、障害物の形状を考慮することで、足部軌跡を上下・左右方向に制御することが可能であると考えられる。本研究では、障害物横断時の足部軌跡が障害物の形状に影響されるかどうかを明らかにすることを目的とした。

2

1.

Mobility is an indispensable ability for survival in animals
Animals must move in search of food. This voluntary animal movement is called

locomotion, which is specific to a specie and closely related to the habitat and its bodymorphology. Animals use various forms of locomotion, such as flying, crawling,swimming, running, and walking. Walking is one of the most common forms oflocomotion among mammals, and humans are the only animals that have acquired
habitual upright bipedal locomotion. Our hominid ancestors began bipedal walking
approximately 6–7 million years ago [1]. One hypothesis that accounts for thisevolutionary adaptation is the lower energy requirement compared to quadrupedalism [2].
However, this remains a hypothesis, and the selection pressure for bipedalism in humans
remains unknown.
Given that humans habitually walk on two legs, they have physicalcharacteristics that distinguish them from other primates. One of the differences in the
body structure of humans and chimpanzees is the shape of the pelvis. Bipedal locomotion
requires the support of the head and the upper body above the ground in humans, whereas
chimpanzees do not. Thus, the iliac wing of a chimpanzee’s pelvis is almost flat, whereas
the human pelvis has evolved such that the iliac wing protrudes widely to the side [3].
Human gait is significantly influenced by the aforementioned unique bodystructure, which results in the rhythmic and alternating movement of the limbs. As a result3

of this rhythmic motion, walking is regarded as a form of stereotypic locomotion.
However, even when the environment is new or unpredictable, humans can adapt
appropriately and perform walking locomotion. Therefore, it is evident that humans
gradually modify their locomotion to adapt to changes in the environment.

2.

Visual information is necessary for humans to perform adaptive walking
When humans perform locomotion in complex environments, visual information

plays an important role in facilitating appropriate adaptation. Obstacle crossing, an
example of adaptive locomotion, is a visually dependent movement [4]. When there is an
obstacle in the walking path, an individual must instantly assess visual information, suchas the relative position, height, and shape of the obstacle, and the distance from the footto the obstacle. Visual and somatosensory information is needed to control the lower
limbs before traversing an obstacle, as well as during the process of stepping over an
obstacle. Moraes et al. (2014) [5] revealed that adjustment of foot placement occurs even
before crossing an obstacle and visual information contributes to the effective motor
control of the lower limb. It has been reported that the trajectory of the leading foot isimmediately modified by visual inspection of the leading limb [6] and that obstaclecrossing behavior is affected by an optical illusion [7,8]. The motion of the lower limb
when crossing an obstacle was evaluated using "clearance," which is the vertical distance4

between the toe and the obstacle [9,10]. Elliot et al. (2009) [7] used an obstacle incombination with a horizontal-vertical illusion to determine how optical illusions affectclearance during the traversal of obstacles. This illusion is one in which a vertical line
segment seems to be longer than a horizontal one, even if they are both the same length[11]. Two obstacles were used in the experiment: one with black horizontal line segmentson the sides of the obstacle and black vertical line segments on the top of the obstacle ("Hcondition"), and the other one with black vertical line segments on the sides and black
horizontal line segments on the top ("V condition"). The results revealed that theclearance for the V condition was larger than that for the H condition. Other researchers
have also reported that the high-contrast black-and-white pattern of the obstacle was thecause of the greater clearance [8].

3.

Clearance depends on the energy consumed and the risk of contact with obstacles
Humans use visual information to control their lower limb movements relative

to the height and shape of an obstacle. Foot elevation is determined by a trade-off between
energy minimization and the risk of obstacle contact (stumbling). Heijnen et al. (2012)[12] reported that the greater the number of trials, the smaller the clearance of the leading
and trailing limbs. They also reported that since contact with obstacles did not increase
with the number of trials, a decrease in clearance may not be due to physical fatigue but
5owing to the achievement of energy minimization. This result suggests that under aguaranteed safety condition, individuals prioritize energy minimization strategies rather
than reducing the risk of obstacle contact. Conversely, the stair climbing task results inhigher clearance to reduce the risk of contact under conditions whereby the memory of
the stair height is obscured by gaze aversion [13].

4.

Interaction of motor control of the lower limbs during walking over obstacles
Previous research on adaptive locomotion has shown that limb movements arecontrolled independently [12,14,15]. The motion and feedback of one limb are not used
to control the other limb. Heijnen et al. (2012) [12] discovered that obstacle contact
occurred more frequently in the trailing leg than in the leading leg. This was interpreted
as the independent control of the leading and trailing limb movements. Moreover, theabsence of visual information when the trailing limb crosses an obstacle results in highfrequency contact. Based on this concept, the interaction of motor control between theleading and trailing limbs during the traversal of obstacles was not an area of focus but
has been discussed for each leading and trailing limb [9,10,16–26]. In addition, from aclinical perspective, certain characteristics such as a narrower step separation, larger toe
clearance, and smaller heel clearance were observed in a high-fall-risk group compared
to a low-fall-risk group. In addition, the symmetry of the leading and trailing limb
6

clearance was lower in the low-fall-risk group compared to the high-fall-risk group [27].
As previously indicated, several reported adaptive walking studies support thetheory that motor control of the leading and trailing limbs are executed independently,
and the evaluation of the leading leg (the first leg to step over an obstacle) and the trailingleg (the last leg to step over an obstacle) are independent. However, previous studies on
performing certain tasks using the upper limb [28–30], the working memory during
obstacle crossing [31], and obstacle crossing in a VR (Virtual Reality) environment [32],suggest that there may be an interaction in the motor control between the leading andtrailing limbs. Reaching movement in the upper limb typically involves left-right limb
movement. Howard et al. examined the effects of lead-in and follow-through movements
on motor memory during an arm extension task [29,30]. They demonstrated that different
motor adaptations were associated with identical arm extension movements whendifferent movements were performed immediately before and after the task. Nozaki et al.
(2006) [28] showed that novel loads learned in one-handed reaching are partially and notcompletely transferred to the unlearned upper limb during two-handed reaching. Thesefindings suggest that motor control during arm-reaching is not limited to the controlled
movement itself, but depends on the movements performed before and afterward, and by
the opposite upper limb. Heijnen et al. [31] showed that during obstacle-crossing gait, the7leading leg is controlled based on obstacle information acquirement from visualassessment, whereas the trailing leg is not controlled based on visual information, but on
working memories about the obstacle formed by the leading leg before crossing. In
addition, Hagio et al. (2020) [32] suggested that the neural resources of limb-specificmotor memories in the obstacle-crossing movements of the leading and trailing legs areshared based on visual input about the obstacle and the trajectory of the limb during thecrossing. These findings suggest that the interaction of the leading and trailing limbs isaccolated with the motor control of the lower limb during obstacle-crossing.

5.

Obstacle shape affects the motor control of the lower limb during obstacle traversal
Typically encountered obstacles are not always the same height on both sides.

For example, the chain connecting two poles in a parking lot is warped in the middle ofthe chain, and the height that the leading and trailing limbs cross is different. How are thelower limbs controlled when an irregularly shaped obstacle is crossed? As previously
indicated, walking over obstacles is visually-dependent locomotion [4]. Patla [9]examined the effects of the height and depth of obstacles on the motor control of the lower
limbs. The participants included six healthy young adults, and the obstacle heights were
6.7 cm, 13.4 cm, and 26.8 cm, and the depths were set at 6.7 cm, 13.4 cm, and 26.8 cm,
8respectively. The results indicated that as the obstacle height increased, the clearance also
increased. Moreover, the change in clearance was small as the obstacle width increased.
Based on these findings, it can be concluded that the shape of an obstacle determinedbased on visual assessment is important for motor control of the lower limb during its
traversal.
Clearance was influenced by time constraints [25], aging [16,26], cognitive
function [19], sex difference [18], and obstacle height and depth [9]. However, any studies
used obstacles of the same height on the left and right sides, irrespective of whether the
obstacle was a hurdle or a box [10]. Therefore, the interaction between the leading andtrailing limbs when crossing obstacles of different heights and shapes remains unclear.
Typical obstacles do not always have simple and regular shapes such as those used inlaboratory experiments, which include rectangles, and the leading and trailing legs may
have to traverse obstacles of different heights. Therefore, it is necessary to conduct an
obstacle-crossing gait study in which the subject traverses obstacles with irregular shapes,
similar to real-world situations. In addition, in walking over obstacles, it is necessary toattain appropriate clearance in the vertical direction to avoid contact with them, dependingon their shape. During the crossing of an obstacle of the same height on the left and rightsides, the risk of foot contact does not change even if the foot is moved in the left or right9

direction within the width of the obstacle if the foot is in the same elevated position.
Therefore, when crossing an obstacle of the same height on the left and right sides, amovement strategy that attempts to reduce the risk of contact with the obstacle bycontrolling the foot in the vertical direction may be utilized. However, when crossing a
trapezoidal obstacle, for which the height differs from left to right and the top of the
obstacle is tilted to either side, the risk of contact with either the little finger or the thumbincreases when the foot is moved in the left or right direction within the width of the
obstacle, even though the foot elevation is the same. Therefore, when crossing anirregularly shaped obstacle such as a trapezoidal obstacle, a movement strategy that
reduces the risk of contact by controlling the foot motion in the mediolateral direction
rather than in the vertical direction should be utilized. As such, it is conceivable thathumans control the lower limb movement in response to different obstacle shapes byadapting their locomotion to the shape of each obstacle.

6.

The hypothesis and objectives of this study
In previous studies, the shape of the obstacle was rectangular, and the height anddepth of the rectangular obstacle had been shown to affect the foot trajectory. However,
obstacles that are typically encountered are not necessarily rectangular but may be
10

irregularly shaped, such as trapezoids. Therefore, the purpose of this study was todetermine whether the trajectory of the foot is influenced by the shape of an obstacle
during its traversal. We hypothesize that (1) there is an interaction in the motor control
between the leading and trailing limbs, (2) obstacle height on the opposite leg side andthe motion of the opposing leg affects clearance, and (3) the motion of the lower limb iscontrolled in the vertical and lateral directions considering the overall shape of the
obstacle.

11

Chapter 2.
Review of the Literature
Abstract
Several studies have shown that the control of walking locomotion acrossobstacles, which can usually be performed without difficulty by normal adults, is acomplex process that involves a wide range of functions. Even if the task appears to be
the same in the sense of crossing an obstacle of the same height, it is completely different
depending on the context, such as the requirement of cognitive resources, the presence ofobstacles, and the shape of the obstacles. Given that there are an infinite number ofvariations in complexity, i.e., the context to incorporate in a study, the contexts that arepresented may not be the most important. It is important to accumulate evidence byresearching to clarify the effects of obstacle shape on foot trajectory, for which evidenceis lacking, among others, to elucidate the underlying mechanisms of postural gait control
and minimize falls in the elderly.

進矢正宏, 三浦有花, 複雑なコンテクストが反映された障害物跨ぎ歩行研究, 理学
療法-臨床・研究・教育, 29(1), 3-10, 2022.
12

Chapter 2.
Review of the Literature
Abstract (in Japanese)
健常な成人であれば問題なく行える障害物を越える歩行運動の制御は、非常に幅広い機能を含む複雑な制御であり、同じ高さの障害物を越えるという意味では同じタスクに見えても、同時に認知資源を必要とするか、他の障害物が存在するか、障害物の形状はどうなっているかなど、コンテクストによって全く異なる運動となることが知られている。すなわち障害物跨ぎ越し歩行は、他の障害物が存在するかどうか、障害物の形状がどのようなものかといった文脈によって、全く異なるものになり得るということである。複雑さのバリエー
ション、すなわち研究に取り入れるべきコンテクストは無限にあるため、本チャプターで紹介したコンテクストが最も重要であるとは限らない。姿勢歩行制
御の根本的なメカニズムを解明と高齢者の転倒を最小限に抑えるためには、中でもエビデンスの不足している障害物の形状が足部軌跡に与える影響を明らかにする研究を行い、エビデンスを蓄積していくことが重要である。

進矢正宏, 三浦有花, 複雑なコンテクストが反映された障害物跨ぎ歩行研究, 理学
療法-臨床・研究・教育, 29(1), 3-10, 2022.

13

1.

Summary
Walking locomotion over an obstacle is a facile task in normal adults that is basedon complex control involving a wide range of functions. Even if a task appears to be thesame in the sense of crossing an obstacle of the same height, it is completely different
depending on various factors such as the presence of other obstacles, the shape of the
obstacle, etc. There are an infinite number of factors that should be considered in obstaclecrossing studies. Lower limb motion during overpass gait is evaluated using "clearance,"
which is the vertical distance between the toe and the obstacle. Clearance is mainly
determined by factors such as age, risk of falling, visual information obtained during thecrossing of obstacles, and the characteristics of the obstacle such as its height and shape.
However, previous studies on overpass gait have not elucidated the effect of obstacle
shape on foot trajectory. Typically encountered obstacles do not always have uniform
height or shape on both sides. Therefore, it is necessary to perform an over-stepping gaitthat is more suited to the typical crossing of irregularly shaped obstacles. In this chapter,
we will introduce the main determinants of clearance in obstacle-crossing studies anddiscuss the need to obtain evidence from the perspective of obstacle shape during traversal.

2.

Adaptive locomotion
Steady walking locomotion is a rhythmic movement in which the leading and14

trailing limbs move forward alternately, and the subcortical central nervous system which
includes the spinal cord and brainstem is thought to play a major role. However,locomotion is not limited to flat ground and must be executed safely in diverse
environments. Such adaptive walking requires contribution from the higher-order central
nervous system, such as the processing of sensory inputs from multiple modalities
including vision, for the perception of the external environment and the estimation ofbody state, as well as memory and prediction.
Several studies have been conducted on a variety of adaptive locomotion thattargets various populations. For example, Sekiguchi et al. (2022) [33] compared walking
on uneven and flat surfaces in stroke patients. Oates et al. (2005) [34] used slippery
surfaces and examined the gait-stopping phase. Liss et al. (2022) [35] conducted a study
on young adults to determine adaptation to walking on a treadmill in an environment
where disturbance is expected. In adaptive walking, the objective is not only to step overan obstacle but also to avoid it [36–42]. Several studies have been conducted based ontasks that specifically reflect contemporary social situations, such as stepping overobstacles while typing text messages on a cell phone [22].

15

3.

Obstacle crossing task
Chen et al. (1991) [43] conducted a study in which 12 young and 12 elderly maleand female subjects, 48 subjects in total, were asked to traverse obstacles with heights of
0 mm, 25 mm, 51 mm, and 152 mm. The results showed that in the high obstacle condition,
the walking speed when crossing the obstacle was slower and the clearance was greater.
There was no significant difference in clearance between the older and younger
participants, but the older participants had a significantly slower walking speed whencrossing obstacles than the younger participants. This result has been interpreted as aconservative strategy of older adults when compared to younger adults. Patla et al. (1993)[9] conducted a study on the height and depth of obstacles. The subjects were six healthy
young adults, and the obstacle heights were set at 6.7 cm, 13.4 cm, and 26.8 cm, and thedepths were 6.7 cm, 13.4 cm, and 26.8 cm, respectively. The results indicated that as theheight of the obstacle was increased, the clearance increased, but the change in theclearance was minor as the width of the obstacle increased. The findings of these classic
studies indicate that lower limb motion in the traversal of obstacles is affected not onlyby the size of the obstacle in terms of height and width but also by age. In addition,
previous studies have shown that motor memory [19,31] and cognitive function [26] arealso affected in over-the-obstacle walking.

16

It is known that the traversal of obstacles requires information such as the
position and size of the obstacle, which is obtained visually and is a motor task with highvisual dependence, including binocular vision [44]. In an investigation by Patla et al.
(2002) [44], the subjects crossed obstacles of different heights placed on a walking pathunder two conditions: binocular and monocular vision. The results showed that clearance
was greater when the subjects crossed the obstacle using monocular vision compared towhen they crossed using binocular vision. These results suggest the possibility that the
subjects need to raise their feet higher to ensure clearance because they could not assess
the exact size of the obstacle using monocular vision, or that the obstacle simply appeared
larger than it was in this case. This indicates the importance of obtaining accurate
information about obstacles. In addition, during walking motion, the eyes are usuallyfocused approximately three steps forward. As such, in adaptive walking tasks such as
walking on a bumpy dirt road or climbing stairs, visual information that was retained asworking memory is used as information about the environment, which is necessary forlower limb control that deviates from a normal walking pattern [13,45]. Such complex
information processing involves numerous cortical brain regions, including the visualcortex, posterior parietal lobes, and motor cortex [46,47].

17

4.

Obstacle crossing task in VR and AR environments
In recent years, VR (Virtual Reality) and AR (Augmented Reality) technologies

have attracted significant attention, and they have been incorporated into obstaclecrossing research. Hagio et al. (2020) [32] asked participants to walk over an obstacle ina VR environment and examined the effect of the visual motion transformation of theleading leg on the foot trajectory of the trailing leg. The results showed that the clearanceof both the leading and trailing legs was greater during the crossing of obstacles in a realenvironment compared to a VR environment. It was also determined that only theclearance of the leading leg exhibited a correlation between the VR environment and thereal environment. They also found that when a visuomotor perturbation was applied only
to the motion of the leading leg during the crossing of a virtual obstacle, a trajectory
correction occurred not only in the toe of the leading limb but also in the toe of the trailinglimb. This suggested that the neural resources for lower limb-specific motor memory for
obstacle-crossing movements of the leading and trailing legs are shared based on visual
input about the characteristics of the obstacle and the trajectory of the limbs during thecrossing. Kim et al. (2019) [48] also discovered that learning to walk across an obstacle
in a VR environment transferred to learning to walk across an obstacle in a realenvironment. Kim et al. taught healthy young adult participants to minimize clearance

18when walking across an obstacle in a VR and a real environment. As a result, they foundthat the clearance during the traversal of obstacles in a VR environment transitioned tothe clearance during the traversal of obstacles in a real environment. Based on this result,they argued that the crossing of obstacles should be performed not only in a realenvironment but also in a safer VR environment. Binaee et al. conducted a study thatinvolved an obstacle-stepping walking task that involved 14 healthy young subjects inboth AR and real environments [49]. The results showed that the clearance of the leadingleg during the crossing of the obstacles in the AR environment was larger compared tothat of the real environment. In addition, the speed of approaching obstacles was lower inthe AR environment compared to the real environment. Based on these findings, it isconsidered that the VR environment has a higher association with the traversal of
obstacles in a real environment than in the AR environment.
The traversal of obstacles in a real environment involves the risk of falling owing
to contact, as well as the problem associated with effects that cannot be eliminated. These
include the brightness of the lighting in the laboratory where the experiment is conducted,
the color of the wallpaper and the floor, and the contrast between the color of the floor
and the color of the obstacles. However, these problems can be addressed in a VR or AR
environment, and experiments can be conducted more safely compared to a real19

environment. It is expected that experiments involving the crossing of obstacles in a safer
VR environment will be conducted more frequently in the future.

5.

Research on obstacle crossing reflecting realistic and complex contexts
In classical studies on obstacle-crossing behavior, an experimental setup was

employed in which participants cross a single obstacle placed in the middle of a walking
path in a laboratory. However, this simplified situation is not typical in the real world, and
it is necessary to control walking behavior to consider the crossing of obstacles for cases
involving complex physical or psychological contexts. For example, the number of
obstacles may not be limited to one, but there may be situations in which multiple
obstacles must be crossed. Krell et al. (2002) [50] conducted an experiment in which
healthy young subjects crossed two obstacles placed 1 m, 1.5 m, and 2 m apart, in addition
to a single obstacle condition. In the single obstacle condition, the relative position of thefoot immediately before crossing the obstacle remained constant, regardless of the
distance from the starting point to the obstacle. In contrast, in the two-obstacle condition,
the position of the trailing leg before crossing the first obstacle was adjusted according to
the distance between the two obstacles. This indicates that the strategy for crossing thesecond obstacle is planned and executed before crossing the first obstacle.

20

Silva et al. (2020) [51] compared crossing strategies for two obstacles in 19
healthy older adults and 19 patients with Parkinson's disease. In this study, two obstacles
were placed 50 cm and 108 cm apart, in addition to a single obstacle condition. The study
focused on the left-right asymmetry of clearance. Note that this index is not theasymmetry of the leading and trailing legs in the same trial, but the asymmetry of theclearance of the trial with the right leg as the leading leg and the clearance of the trial
with the left leg as the leading leg. Thus, this index focuses on the difference between thedominant and non-dominant leg in healthy subjects, and the difference between the sidewith major diseases such as tremors or muscle stiffness, and the side with the minor
disease in Parkinson's disease patients, in terms of the difference in the obstacle-crossing
movement. Silva et al. (2020) [51] suggested that this may be the result of age-related
decline in motor, cognitive, and sensory systems, as well as Parkinson's disease. The
Parkinson's disease patients exhibited more asymmetry in clearance, especially in the
trailing limb compared to the healthy elderly group. The location of the second obstacle
was also shown to affect the clearance asymmetry, and Silva et al. (2020) [51] speculated
that the trailing limb clearance asymmetry may be the result of the interference ofsensorimotor processing of the second obstacle and the processing for the first obstacle.
The task of crossing multiple obstacles has been studied not only in patients with21

Parkinson's disease but also in healthy subjects to determine the effects of distance
between the obstacles and age on the traversal of multiple obstacles. Wang et al. (2020)[52] conducted a study in which healthy young adults performed a task wherein they eachcrossed two differently spaced obstacles while walking, to determine their crossing-overmotor strategies. It was demonstrated that the vertical distance from the heel of the leading
leg to the obstacle was greater and the vertical distance from the toe of the trailing leg tothe obstacle was shorter for the second obstacle compared to the first obstacle. Several
studies have compared the crossing of obstacles in normal subjects. Berard et al. (2006)[53] performed a task in which 7-year-old children and young adults were asked totraverse two obstacles while walking. They found that the adults used a consistent
locomotor strategy when the number of obstacles increased, whereas the children used a
conservative locomotor strategy of adjusting the placement of their feet. These findings
indicate that the number of obstacles influences the overpass walking strategy.
Human gait, which involves walking on two unstable legs, is thought to involvea relatively greater role of the higher central nervous system compared to quadrupeds. In
addition, it is known that interference effects such as a reduction of walking speed can beobserved in walking movements when a subject is required to simultaneously perform
cognitive tasks such as mental arithmetic. The degree of interference in the dual-task

22

environment is known to be greater in older adults who have experienced falls [54], andwas thought to reflect the reduced capacity of the central nervous system for processing
in a high-risk group for postural gait control. The performance on the dual task has been
described as a promising predictor of future fall risk [55]. As previously indicated, since
adaptive locomotion is thought to place a greater load on the higher central nervous
system compared to steady walking, several dual-task experiments have been conductedin which the obstacle-crossing task was performed simultaneously with a cognitive task.
Soma et al. (2011) [54] divided elderly subjects into two groups, one with the experienceof falling and one without the experience of falling, and walking was performed. The
results showed that under the dual task condition, the clearance was smaller, and the footwas closer to the obstacle in the group with the experience of falling.
Jehu et al. (2019) [56] conducted a study in which 16 healthy young adults wereasked to hold both a transparent box with no visual information restriction and an opaquebox with visual information restriction. They compared the toe clearances for bothsituations and asked the subjects to step over a 20 cm high obstacle. The results showedthat walking with the opaque box during obstacle crossing significantly increased
clearance compared to walking without the box. In addition, walking with the opaque box
significantly increased clearance compared to walking with the transparent box. In

23addition, walking with the transparent box significantly increased clearance compared towalking without the box. Jehu et al. [56] attributed the increase in the clearance height tothe fact that carrying the box limited visual information about the obstacle to one or two
steps before it was crossed. They also noted that walking with a loaded opaque box may
have increased the difficulty of achieving clearance because of the partially narrowed
visual field of the lower limb, making it difficult to calculate the distance to the obstacle.
Thus, Jehu et al. [56] argue that carrying a load when stepping over an obstacle and thenarrowing of the visual field increase the risk of falling. The increased risk of falling insuch a complex environment compared to simple obstacle-crossing with a single obstaclesuggests the need for experiments on obstacle traversal in complex environments that
better reflect typical scenarios.

6.

The purpose statement of the research
Since there are an infinite number of factors that should be reflected in obstacle-crossing gait research, the determinants of clearance introduced in this chapter are notnecessarily the most important ones. As the findings presented in this chapter show,
previous obstacle-crossing studies have used rectangular obstacles of the same height on
both sides, and there is a lack of data related to the shape of an obstacle. Therefore, the24purpose of this investigation is to evaluate the effect of obstacle shape on clearance, notonly rectangular obstacles, but also stair-shaped obstacles of different heights on the left
and right sides, and trapezoidal obstacles.

25

Chapter 3.
Foot clearance when crossing obstaclesof different heights with the lead and trail limbs(Experiment 1)
Abstract
To predict and prevent falls and fall-related injuries, it is crucial to understandthe motor control for crossing obstacles. In real life, since obstacles do not always takeregular shapes like rectangles, the lead and trail limbs sometimes need to negotiate
different obstacle heights. The interlimb interaction in this process has remained unknown
since obstacle-crossing studies commonly use a single-obstacle paradigm in which the
obstacle height is the same for the lead and trail limbs. We used a dual-obstacle paradigm
to test whether the foot clearance over one obstacle was influenced by the contralateralobstacle’s height. Sixteen healthy young male and female participants (age: 22.5 ± 1.9
years) crossed over two obstacles placed side by side. Four obstacle conditions were madeby combining obstacles of two heights (low, L, 9.0 cm; high, H, 22.5 cm) of the obstacles.
In the LL condition, both obstacles were low, and in the LH condition, there was a low
obstacle for the lead limb and a high one for the trailing limb. Similarly, we also arranged
HL and HH conditions. Each subject performed twenty trials per condition. We compared
the vertical foot clearance, prestep distance, and poststep distance between the conditions.
The foot trajectory to step over the obstacles was affected by the contralateral obstacle’s
height. The vertical foot clearance of the trailing limb was greater in the HL condition
than in the LL condition. The vertical foot clearance of the lead limb was greater in the
LH condition than in the LL condition. The results suggested that the foot trajectory was
not determined exclusively by the obstacle to be crossed. Instead, comprehensive
information, including the height of the obstacle for the other limb, might be used for
motor control during obstacle crossing.

Yuka Miura, Masahiro Shinya, Foot clearance when crossing obstacles of different
heights with the lead and trail limbs, Gait & Posture, 88, 155–160, 2021.

26

Chapter 3.
Foot clearance when crossing obstaclesof different heights with the lead and trail limbs(Experiment 1)
Abstract (in Japanese)
転倒や転倒に関連する傷害を予測・予防するためには、障害物を越えるための運動制御を理解することが重要である。実生活において、障害物は必
ずしも長方形のような規則的な形状をしていないため、時として左右で異なる
高さの障害物を跨ぐ必要がある。しかし、障害物跨ぎ越し研究では、障害物の高さが同じである単一障害物実験が一般的であるため、この過程における左右脚間の相互作用は不明なままであった。そこで、我々は 2 障害物実験を行い、一方の障害物を越える際の足のクリアランスが、他方の障害物の高さに影響されるかどうかを検証した。健康な若い男女 16 名（年齢：22.5±1.9 歳）が、並置された 2 つの障害物の上を横断した。障害物の高さを 2 種類（低、L, 9.0cm、高、H, 22.5cm）を組み合わせて 4 つの障害物条件を作成した。LL 条件では両方の障害物が低く、LH 条件では先行脚に低い障害物、後続脚に高い障害物が配置された。同様に、HL 条件と HH 条件も配置した。各参加者は 1 条件につき 20 回の試行を行った。条件間でクリアランス、踏み切り前のつま先から障害物までの水平方向の距離、踏み切り後のつま先から障害物までの水平方向の距
離を比較した。足部軌跡は、反対脚が跨ぐ障害物の高さに影響された。HL 条
件では LL 条件よりも後続脚のクリアランスが大きくなった。また，先行脚のクリアランスは LH 条件で LL 条件よりも大きくなった．この結果から、足部
軌跡は横断する障害物のみによって決定されているわけではないことが示唆された。むしろ、反対脚の障害物の高さを含む総合的な情報が、障害物横断時の運動制御に利用されている可能性がある。

Yuka Miura, Masahiro Shinya, Foot clearance when crossing obstacles of different
heights with the lead and trail limbs, Gait & Posture, 88, 155–160, 2021.

27

Introduction
A survey showed that 35% of elderly people reported at least one fallexperience in the preceding year, and falls may have a detrimental impact on health,independence, and quality of life [57]. One of the causes of falls is tripping overobstacles [58–61]. To predict and prevent such falls, scientists have investigatedstrategies and mechanisms of obstacle crossing [62]. In previous studies on obstacle
avoidance, the distance from the foot to an obstacle, often called clearance, has beenused as a critical parameter in a variety of obstacle-crossing tasks [10,12,31,62,63].
Although these studies used a single obstacle with a certain height and regularshape, real-life environments are complex, and obstacles do not always take regularshapes like rectangles. In such situations, the lead limb and trail limb must negotiate
different obstacle heights. Studies of obstacle crossing have commonly used a singleobstacle paradigm in which the height of the obstacle was the same for the left and right[10,64]. In a paradigm with a single, regularly shaped obstacle, the interaction between
the lead and trail limbs cannot be studied. Assessing the interactive control of lead andtrail limbs when we face environmental challenges (i.e., an obstacle whose height isdifferent on both sides) may help to deeply understand the ability to obstacle avoidance,
contributing to preventing tripping over an obstacle.

28

Recent studies in arm-reaching tasks may provide some insights into thecontrol of the leading and trailing limbs. Howard and his colleagues tested the effect oflead-in and follow-through movements on the motor memory of an arm-reaching task
[29,30]. They demonstrated that different motor adaptations could be associated withphysically identical arm-reaching movements if different movements were performed
just before or after the task. Nozaki et al. (2006) [28] demonstrated that learning a novel
load during unimanual reaching was partially, but not completely transferred to thesame limb during bimanual reaching. They also reported that one could learn two
conflicting force fields if one of them was associated with unimanual and the other withbimanual reaching. These findings suggest that motor control of arm-reaching was not
limited to the controlled movement itself but was dependent on the movements that are
performed before or after it or performed by the contralateral limb. If this concept canbe extended to gait tasks, motor control of the trail/lead limb crossing over an obstacle
might be influenced by the movement of the lead/trail limb.
The purpose of this study was to investigate the interlimb interaction in the
motor control of limb trajectories during obstacle crossing. We developed a dualobstacle paradigm in which the heights of the obstacle were not necessarily the same forthe lead and trail limbs to this end, we established four experimental conditions as

29

combinations of high and low obstacles (i.e., low-low, low-high, high-low, and highhigh) and compared toe clearances between the conditions. We assumed that if the
motor control of one limb would be affected by the other side, one would expect
different limb trajectories for crossing the same obstacle depending on the height of thecontralateral obstacle.

Methods
Participants
Sixteen young, healthy adults participated in this study (eight males and eightfemales; age: 22.5 ± 1.9 years; height: 165 ± 9.5 cm; weight: 58.2 ± 9.6 kg). Eachsubject’s dominant foot was determined using a modification of the Waterloo
Footedness test of Melick et al. (2017) [65]. Fifteen participants were right-footed, andone was left-footed. Participants were free from any impediments to normal
locomotion and had normal or corrected-to-normal vision. All participants gave written
informed consent, and the study was approved by the local ethics committee ofHiroshima University in Hiroshima, Japan (approval number: 01-31), according to the
Declaration of Helsinki.

30

Experimental protocol
Participants walked barefoot at a self-selected pace along a 7 m walkway andstepped over obstacles. Two obstacles were placed in the middle of the walkway. The
participants were instructed to cross the obstacle with the right leg (lead leg) in the fifth
step and with the left leg (trail leg) in the sixth step (Figure 3-1-A). Before theexperiment, the participants were asked to adjust the starting position without actuallycrossing over the obstacles. Two different obstacle heights were used (Figure 3-1-B):
low (height: 9.0 cm; depth: 29.7 cm; width: 21.0 cm) and high (height: 22.5 cm; depth:
29.7 cm; width: 21.0 cm). Four experimental conditions were arranged by combining
the two heights. The condition where the low obstacle was set for the lead leg and thetrail leg was termed LL. Similarly, we arranged LH, HL, and HH conditions (Figure 31-C). It has been reported that there is a learning effect on stepping parameters in
obstacle-crossing studies in the previous study [12]. In the present study, to assess thepotential learning effect, we recorded twenty trials for each condition (80 trials in total).
No practice trials were conducted before the experimental sessions. The order of theconditions was randomized between the participants.

31

Figure 3-1. Experimental setup. A. Participants were asked to walk on a walkway andcross over obstacles at the 5th and 6th steps. The right leg was always the lead leg(gray). B. Dimensions of the obstacles. We used two obstacles with different heights:
22.5 cm (High: H) and 9.0 cm (Low: L). C. Experimental conditions. We tested fourcombinations of obstacles (LL, HL, LH, and HH). The grey boxes indicate the obstacles
for the lead (right) leg and the white boxes indicate the obstacles for the trail (left) leg.
Note that panel A shows the LH condition.

Data collection
We measured the stepping kinematics of each experimental condition. Infrared
reflective markers were pasted on sixteen anatomical landmarks on each participant’s
body: the left and right medial femoral epicondyle, lateral femoral epicondyle, medial

32malleolus, head of the first metatarsal, head of the fifth metatarsal, and calcaneus. The
markers were captured by a 3D optical motion caption system (Qualisys Track
Manager, Qualisys, Göteborg, Sweden) with eight cameras (Qualisys-Miqus M3,
Qualisys). The sampling frequency of the kinematic data was 250 Hz. The measured
signals were stored on a computer, and all numerical calculations were performed using
MATLAB 2017b (Math Works, Inc., MA, USA).

Data analysis
In one trial, a participant hit the obstacle with the lead leg in the LH condition.
Six participants hit the obstacle with the trail leg in the HL (1 trial), LH (3 trials), and/or
HH (3 trials) conditions. The number of obstacle strikes was larger for the high obstacle
than for the low obstacle and larger for the trailing limb than for the lead limb. These
trials were excluded from the subsequent analyses.
The kinematic data were low-pass filtered using a zero-lag second-order
Butterworth digital filter with a cutoff frequency of 20 Hz. The cutoff frequency wasdetermined based on the visual inspection of the experimenter so that the filtered signals
reflect the characteristics of the raw data being free from the effect of the noise. The
limb trajectory during the obstacle avoidance was quantified for the lead and trail legs

33

by using the following parameters (Figure 3-2). The vertical foot clearance was definedas the distance between the marker placed at the first metatarsal marker and the top of
the obstacle when the marker was just above the obstacle. Note that in the calculation of
the foot clearance, the vertical offset of the toe marker was compensated. We calculated
the prestep and poststep distances.

Figure 3-2. Illustration of the vertical foot clearance, prestep distance, and poststep
distance. The gray box indicates the obstacle, and the dashed line indicates the trajectoryof the leg as the participants crossed over the obstacle.

Statistics
In this study, since we were interested in the effect of the height of thecontralateral obstacle on the limb trajectory, we examined pairs of conditions where theheight of the obstacle for the lead/trail leg was the same and the contralateral obstacle
34

was different. For instance, the height of the obstacle for the lead leg was the same
between the LL and LH (i.e., the lead leg crossed over the low obstacle in bothconditions), whereas the obstacle height for the trail leg was different. Similarly, we
compared the lead leg trajectories between the HL and HH conditions, and wecompared the trail leg trajectories between the LL and HL conditions and between the
LH and HH conditions. Because the toe clearance could be decreased as one repeats
trials [12], we calculated 5-trial averages of the clearances (i.e., trial numbers 1-5, 6-10,
11-15, and 16-20 were averaged). To test the effects of the obstacle condition and therepetition of the trials on the outcomes, we used two-way repeated-measures ANOVAs(condition * trial). Once a significant interaction was observed, the differences between
the obstacle conditions were tested for each of the four epochs of trials. The significancethreshold was set to 0.05 for the ANOVAs and Bonferroni correction was used for the
posthoc comparisons (0.0125 = 0.05/4). The statistical analyses were performed using
JASP (Eric-Jan Wagenmakers, Amsterdam, Netherlands).

Results
The limb trajectories during obstacle crossing were affected by the height ofthe contralateral obstacle. The limb trajectories of a typical subject and statistical results

35

for the foot clearance are illustrated in Figure 3-3 and Figure 3-4. The descriptive andstatistical results for all parameters tested are summarized in Table 1.
The 2-way rmANOVA (LL/HL * trial) revealed that the trail limb trajectory
was different between the LL and HL conditions (Figure 3-3-A, C). The participants
lifted their trail limb higher in the HL condition than in the LL condition, which was
confirmed by the significant main effect of the condition on foot clearance (F (1, 45) =5.18, p = 0.04, η 2 = 0.26). A significant main effect of the trial (F (1, 45) = 4.38, p =0.01, η 2 = 0.23) indicates that the foot clearance of the trailing limb decreased as
subjects repeated the task in the LL and HL conditions. The prestep distance of thetrailing limb was longer in the LL condition compared with the HL condition (F (1, 45) =8.02, p = 0.01, η 2 = 0.35).
As a result of the 2-way rmANOVA (LH/HH * trial), no significant difference
between the LH and HH conditions was observed on the foot clearance of the trailinglimb. The condition * trial interaction was significant in the prestep distance. The multiple
comparisons show that the LH condition was significantly more significant than the HH
condition in prestep distance for Trial 16-20 (p < 0.05).

36

Figure 3-3. Measurement of the foot clearance for the trailing limb. A, B: The trajectoriesof the marker attached to the head of the first metatarsal of the trail foot for one participant
are superimposed. The gray box indicates the obstacle. C, D: The mean values of all
subjects and 95% confidence intervals of the foot clearance.

The comparison between the LL and LH conditions revealed that the lead limb
trajectory was also influenced by the obstacle height for the trailing limb (Figure 3-4-A,

37

C). The lead limb was lifted higher in the LH condition than in the LL condition (F (1, 45)= 7.43, p = 0.02, η 2 = 0.33). A significant main effect of the condition was also observedin the poststep distance (F (1, 45) = 10.1, p = 0.01, η 2 = 0.40). The lead leg clearance
decreased with repetition in the LL and LH conditions, which was confirmed by thesignificant main effect of the trial on the foot clearance (F (1, 45) = 5.75, p < 0.01, η 2 =0.28). The poststep distance of the lead limb was longer in the LL condition than in the
LH condition. In the 2-way rmANOVA (LL/LH * trial), a significant interaction wasobserved on the prestep distance (F (3, 45) = 6.31, p < 0.01, η 2 = 0.30). Multiple
comparisons showed no significant differences between the LL and LH conditions.
No significant main effects or interactions were observed in the comparison of
the lead limb trajectories between the HL and HH conditions except that poststep
distance was larger in the HL condition than in the HH condition (F (1, 45) = 15.3, p <0.01, η 2 = 0.50).

38

Figure 3-4. Measurements of the foot clearance with the lead limb. A, B: The trajectoriesof the marker attached to the head of the first metatarsal of the lead foot for one participant
are superimposed. The gray box indicates the obstacle. C, D: The mean values of all
subjects and 95% confidence intervals of the clearance.

39

40

Interaction
η²pF
M.E. of Trial
η²p
F

M.E. of Obstacle
η²pFInteraction
η²pF
M.E. of Trial
η²p
F
M.E. of Obstacle
η²pF

3.33 0.03 0.18
0.10 0.96 0.01

1.65 0.19 0.10
1.05 0.38 0.07

3.97 0.07 0.21
2.49 0.14 0.14

158 ± 33949 ± 73

162 ± 30953 ± 79157 ± 31952 ± 78164 ± 34946 ± 86

182 ± 44926 ± 64

178 ± 39935 ± 80168 ± 38934 ± 75

170 ± 38923 ± 65

Horizontal distance before obstacle

Horizontal distance after obstacle

Table 3-1. Descriptives statistics and ANOVA of the foot clearance, prestep distance, and poststep distance.

1.04 0.38 0.07
9.77 < .001 0.39
1.38 0.26 0.08

121 ± 50127 ± 43131 ± 50137 ± 54125 ± 58

133 ± 57

146 ± 72

159 ± 60

Foot clearance

Trail limb in condition HH
11-15
6-10
16-20

Trials 1-5

16-20

0.30 0.82 0.02
1.52 0.22 0.09

0.42 0.53 0.03

977 ± 59972 ± 64967 ± 79962 ± 72966 ± 61958 ± 64962 ± 68957 ± 65

Horizontal distance after obstacle
Trial limb in condition LH
11-15
6-10

0.39 0.76 0.03
0.43 0.74 0.03

8.02 0.01 0.35

136 ± 24

141 ± 30143 ± 28

143 ± 33

Trials 1-5

1.90 0.14 0.11
4.38 0.01 0.23

5.18 0.04 0.26

101 ± 35

108 ± 41112 ± 45

122 ± 4785 ± 32
156 ± 33

88 ± 27156 ± 32

87 ± 32
156 ± 3090 ± 26

156 ± 35

Foot clearance

Horizontal distance before obstacle

Trail limb in condition HL
11-15
6-10
16-20

Trials 1-5

16-20

0.14 0.93 0.01

0.27 0.85 0.02

15.3 0.00 0.50

337 ± 26338 ± 24341 ± 24340 ± 29355 ± 36354 ± 37355 ± 36357 ± 31

Horizontal distance after obstacle
Trail limb in condition LL
11-15
6-10

0.21 0.89 0.01

0.48 0.70 0.03

3.60 0.08 0.19764 ± 89771 ± 74761 ± 78756 ± 90754 ± 64750 ± 80746 ± 78741 ± 81

Trials 1-5

0.76 0.52 0.05

0.99 0.41 0.06

3.55 0.08 0.19

135 ± 31137 ± 32

137 ± 30141 ± 30142 ± 34

144 ± 39144 ± 38

143 ± 35

16-20

Horizontal distance before obstacle

Interaction
η²pF

M.E. of Trial
η²pF

Foot clearance

16-20

1.30 0.29 0.08

1.34 0.27 0.08

10.1 0.01 0.40
M.E. of Obstacle
η²pF

300 ± 38305 ± 39309 ± 32309 ± 30333 ± 34327 ± 35

331 ± 36334 ± 42

Horizontal distance after obstacle
Lead limb in condition HH
11-15
6-10
Trials 1-5

6.31 0.00 0.30

3.36 0.03 0.18

0.00 0.95 0.00

792 ± 85782 ± 92762 ± 77744 ± 97

767 ± 80768 ± 67773 ± 74

770 ± 82

Horizontal distance before obstacle

Lead limb in condition HL
11-15
6-10
Trials 1-5

2.23 0.10 0.13

5.75 0.00 0.28

7.43 0.02 0.33

127 ± 35132 ± 37

137 ± 37

142 ± 36

Interaction
η²p

111 ± 19

F

M.E. of Trial
η²p
F

M.E. of Obstacle
η²
p
F

16-20

111 ± 18

Lead limb in condition LH
11-15
6-10

114 ± 21

Trials 1-5

16-20

116 ± 22

Lead limb in condition LL
11-15
6-10

Foot clearance

Trials 1-5

Discussion
In this study, we compared the clearance of the lead and trail legs whencrossing over side-by-side obstacles of unequal heights. We observed that the foottrajectory when crossing obstacles were affected not only by the height of the obstacle
to be crossed but also by the contralateral obstacle in which the preceding or thefollowing step was made. An interesting feature of the results was the asymmetry of theeffect of the contralateral obstacle: the lead limb clearance over the low obstacle waslarger when the trail obstacle was high (LH condition) and it was smaller when the trail
obstacle was low (LL condition), whereas the lead limb clearance over the high obstacle
was not influenced by the contralateral obstacle's height (no difference between the HL
and HH conditions). A similar effect was also observed in the trailing limb. Since footclearance is the safety margin in the obstacle-crossing task, decreasing the clearance
might lead to a higher risk of tripping. The observed asymmetric effect of thecontralateral obstacle on foot clearance might be explained by the safety-first principleof gait and posture motor control: the primary goal of gait and posture control is to
avoid falls and fatal fall-related injuries [4]. Psychological studies have suggested thataffordance for adaptive locomotor tasks such as stair climbing and obstacle crossing isestablished not only by using the information of the object itself (i.e., stair or obstacle)

41but also by integrating various information such as the surrounding environment and thesubject’s motor capabilities [66,67]. Our result might reflect the comprehensive
information processing that takes place to control gait and posture safely.
The result that the trajectory of the lead limb was affected by the height of thetrail obstacle was not explained by the sequential interlimb interaction, but it suggests
the predictive motor control based on the given environment. Motor adaptation
experiments have suggested that the same arm-reaching movement might be represented
in different ways in the motor system depending on contextual factors such as the
movement of the other limb or movements performed immediately before or after the
focal reaching movement. Nozaki et al. (2006) [28] demonstrated that learning a novel
load during unimanual reaching is partially but not completely transferred to the samelimb during bimanual reaching. They also reported that the learned dynamics wererevealed only by the original context (i.e., unimanual or bimanual) and found that
subjects could learn two conflicting force fields if one were associated with unimanualand the other with bimanual reaching. Howard and his colleagues demonstrated thatdifferent lead-in or follow-through movements accompanied by a kinematically
identical arm-reaching movement formed different motor representations of the same
arm-reaching movement [29,30]. Hagio et al. (2020) [32] revealed that visuomotor

42

processing was shared between lead and trail limbs in their motor learning experimentusing obstacle-crossing tasks in a VR environment.
Based upon the above studies, we discuss that the central nervous systemprocesses the visual information of the given environmental context including obstacleswith different heights, and controls the foot clearance of the lead and trail limbs tonegotiate the obstacles. The results of the prestep and poststep distances also suggestthat the lead and trail limbs are not controlled independently but comprehensively. The
prestep distance of the trail (left) limb was longer in the LL condition than in the HL
condition. The result means that the participants placed the left foot far away from the
obstacle when the right leg was to cross the low obstacle and placed the left foot close
to the obstacle when the right leg was to cross the high obstacle. The consistent results
were observed in the poststep distance of the lead (right) limb in the comparison
between the LL and LH conditions and between the HL and HH conditions. Pearson etal. (2015) [68] reported the anteroposterior hip-to-toe distance was biomechanicallyrelated to the toe trajectory slope: a long hip-to-toe distance would yield a shallow
slope, and a short distance would yield a steep slope. The participants in this study
might take into account the control of the contralateral limb to determine theanteroposterior foot placements.

43

Although we analyzed only the foot trajectories in this paper, the foot trajectoryof the swing limb results from the coordination of multiple joints, including joints in the
support limb, trunk, and swing limb. In the comparison between HL and LL conditions,for example, the difference in the height of the obstacle for the lead limb might
influence the position and velocity of the hip at the takeoff of the trailing limb to crossthe low obstacle. Different swing durations owing to different obstacle heights could
also affect the state of the body. For example, the swing duration of the lead limb would
be longer in the HL condition than in the LL condition because the obstacle on the leadlimb side was higher. The elongation could affect the positions and velocities of the hipand trunk. Biomechanically detailed measurements and analyses would be required toinvestigate such questions.
It would also be interesting to study the behavior of older people in a similar
obstacle-crossing task, where the lead and trail limbs cross obstacles of different
heights. Many studies have reported physical and cognitive deficiencies in elderly
people such as reduced muscle strength, reduced joint flexibility, and impaired working
memory [13,31,47]. Recent studies have reported that even healthy older adults areunaware of their age-related physical decline and have difficulty in appropriately
gauging the relationship between their physical ability and their environment [26,69].

44

Cognitively impaired older adults showed lower trailing limb clearance and thus greaterfoot clearance asymmetries than young adults [70]. This is because, due to its invisible
movement, stepping over an obstacle with the trailing limb is mostly guided by theworking memory of the obstacle height [71]. Obstacles in daily living are not always
symmetrically or regularly shaped. Our results revealed the comprehensive interlimb
motor control for negotiating such a complex environment, suggesting that studies using
a simple obstacle might not be sufficient to assess the real-life risks in adaptive
locomotion. Although this study only used healthy young volunteers, studies on people
with a large asymmetry and/or cognitive impairments, such as the elderly population,
stroke survivors, and Parkinson’s disease, would shed light on how physical andcognitive decline affects obstacle crossing in the complex environment.

Conclusions
In conclusion, the trajectory of a limb in crossing over an obstacle was affected
not only by the height of the obstacle to be crossed but also by the obstacle on the otherside. This suggests that there is an interaction between the lead and trail limbs in the
motor control system. And also, It is expected that research on people with a highasymmetry of leading and trailing limb movements in obstacle avoidance gait, such as

45

Parkinson's disease patients [51]. It would be interesting for future studies to take this
into account and investigate how the foot trajectory is controlled for fall prevention in
the elderly.

Funding
This study was supported by JSPS KAKENHI Grant Number 17H04750.

46

Chapter 4.
The shape of the obstacle affects the left-right trajectoryof the lower limb when stepping over the obstacle(Experiment 2)
Abstract
In previous studies of crossing over obstacles, vertical foot clearance has beenused as an indicator of the risk of contact. Under normal circumstances, people do notalways step over obstacles of the same height on both sides, and depending on the shapeof the obstacle, the risk of contact may differ depending on the foot elevation position.
Therefore, the objective of this investigation is to determine the influence of the shape ofan obstacle on the positioning of the foot. Sixteen healthy young adults performed a task
in which they crossed over two obstacles with different shapes: a trapezoidal obstacle anda rectangular obstacle, as viewed from the frontal plane while walking. The results
showed that when crossing over a trapezoidal obstacle, the participants-maintained footclearance by controlling the mediolateral direction, which reduced the height of the
obstacle. The results of this study suggest that lower limb movements during walking
over an obstacle are controlled not only in the vertical direction but also in the
mediolateral direction by controlling the foot trajectory to reduce the risk of contact. It
was demonstrated that the control was comprehensive, considering the shape of the
obstacle, including the opposite limb.

Yuka Miura, Kohei Yoshimoto, Masahiro Shinya, The shape of the obstacle affects theleft-right trajectory of the lower limb when stepping over the obstacle, Frontiers in
Sports and Active Living (under review).
47

Chapter 4.
The shape of the obstacle affects the left-right trajectoryof the lower limb when stepping over the obstacle(Experiment 2)
Abstract (in Japanese)
これまでの障害物跨ぎ越し歩行研究では、鉛直方向のクリアランスを障害物との接触リスクの指標として用いてきた。日常生活では必ずしも左右で一様な高さの障害物を跨ぐとは限らず、障害物の形状によっては足部の挙上位
置に応じて、障害物との接触リスクが異なる可能性がある。そこで本研究では、
障害物の形状によって足部がどのように制御されているかを明らかにすることを目的とした。健常な若年成人 16 名を対象に、歩行中に前額面から見て台形の障害物と長方形の障害物の 2 つの形状の障害物を跨ぐ課題を実施した。その結果、台形の障害物を跨ぐ際は、障害物の高さが低くなる左右方向の制御を行うことでクリアランスを確保していることが示された。本研究の結果から、障害物跨ぎ越し歩行における下肢の運動は、鉛直方向だけではなく左右方向の足部軌跡の制御を行うことで、接触リスクを下げる戦略を行い、反対脚も含めた障害物全体の形状を考慮に入れた包括的な制御を行っていることが示唆された。

Yuka Miura, Kohei Yoshimoto, Masahiro Shinya, The shape of the obstacle affects theleft-right trajectory of the lower limb when stepping over the obstacle, Frontiers in
Sports and Active Living (under review).
48

Introduction
Falls can have a deleterious effect on health, independence, and quality of life
across all ages [72]. One of the causes of falling is contact with obstacles [60,61,72,73].
To predict and prevent falls, scientists have investigated the foot trajectory during obstacle
traversal [10]. In previous obstacle-crossing studies, the vertical foot clearance i.e., thevertical distance between the foot and an obstacle, has been used as a main kinematic
outcome [10,16,51,74,75]. Clearance has been used to assess the risk of contact between
obstacles and the foot. It was revealed that the clearance was affected by the risk of falling[27], and the effects of aging [16]. Clearance during the traversal of obstacles has also
been used as an indicator of improvement in adaptive walking ability in stroke patients[76]. Based on these findings, clearance is often used in clinical practice as a measure ofwalking ability associated with certain diseases or aging.
It is known that foot clearance depends on the obstacle’s properties such as height
and location. However, it has also been shown that clearance is influenced by theenvironment in which walking is performed. Clearance increases with the height of the
obstacle, and also, it was clear that the clearance was greater when the pattern of the
obstacle to be crossed was vertical compared to a horizontal pattern [7]. In addition, thecolor contrast of obstacles was another factor that impacted clearance, and it has been49

reported that the high contrast of the colors black and white also resulted in greater
clearance [8]. Heijnen et al. (2012) [12] found that clearance decreased during repeatedobstacle-crossing tasks.
The results of previous research suggest that foot clearance was determinedbased on the tradeoff between energy consumption to control the lower limb and the riskof contact with an obstacle. Although the basic principle of motor control is energy
minimization [12], a zero-clearance trajectory is not optimal considering inherent
sensorimotor noise and the risk of contact with obstacles. Instead, the central nervous
system plans the trajectory of the foot to maintain a certain clearance as a safety margin.
For example, Shinya et al. (2012) [13] reported that stair-climbing tasks resulted in higher
clearance under conditions in which the memory of stair height was obscured by averted
gaze. Most previous studies focused on the foot trajectory in the sagittal plane (i.e.,
vertical foot clearance), however, the influence of obstacle traversal on the mediolateralfoot position during walking should also be investigated.
Lower limb movements in obstacle crossing were controlled based on energy
minimization strategies [12], and Slawinski et al. (2012) [77] reported that in healthy
participants, the more the foot was elevated, the greater the energy expenditure. Although
there are no studies that quantitatively estimate the energy expenditure associated with50

the vertical MP1 position during obstacle crossing, the results presented to date suggestthat this position is more efficient in the lateral direction compared to the vertical directionin achieving the same amount of foot clearance. Although the risk of contact with the
obstacle and energy consumption must be considered in obstacle-crossing, postural
stability must also be considered. Yamagata et al. (2021) [78] reported that excessive footelevation in obstacle-crossing would induce postural instability in the mediolateral
direction. Accordingly, a safer strategy for the crossing of irregularly shaped obstacles
should be adopted, such as increasing the MP1 position in the mediolateral direction to
reduce the risk of contact with the obstacle, instead of reducing the risk of contact byelevating the foot.
In previous studies, since the obstacle height was the same in the mediolateral
direction, the foot clearance and the risk of collision would not change with themediolateral foot movement. In this case, the control of the foot position is relevant onlyin the vertical direction. In contrast, if an obstacle is trapezoidal in the frontal plane andthe top edge is tilted in the mediolateral direction, the mediolateral foot position would
be task-relevant. For instance, if the top edge of an obstacle is right-up-left-down, moving
the foot leftward would increase the clearance even if the vertical elevation is the same.
As such, it is not clear if the mediolateral foot position is influenced during obstacle
51

crossing. In this study, we used trapezoidal obstacles, of which the top edge was not flatbut tilted in the frontal plane, as well as a rectangular obstacle (Figure 4-1). Since the footwas moved in the mediolateral direction, it was expected that the radial clearance between
the foot and the trapezoidal obstacles would be maintained.

Methods
Participants
The inclusion criteria for participants of the study included the absence ofimpediments to normal locomotion and the requirement of normal or corrected-to-normal
vision. As exclusion criteria, the participants must not have neurological or
musculoskeletal disorders. An a priori power analysis was performed based on repeated
ANOVA tests using G*power 3.1.9.7. The parameters for the power analysis were set as
follows: effect size f = 0.30, alpha = 0.05, 1-beta = 0.8, number of groups = 1, number ofmeasurements = 7, correlation among measures = 0.50, and non-sphericity correction e =1. The effect size f was obtained from the vertical clearance observed in our previous
report [79]. The suggested sample size was twelve. Conservatively, we recruited sixteen
healthy young volunteers (eight males/eight females; age: 21.3 ± 1.7 years; height: 165.6± 7.9 cm; weight: 59.6 ± 9.9 kg, mean ± standard deviation). All subjects gave written
informed consent before participation, and the ethics committee of the Graduate School52

of Integrated Arts and Sciences, Hiroshima University, approved the study (approval
number: 02-30) according to the Declaration of Helsinki.

Experimental protocol
Each volunteer walked at a self-selected pace on a 7 m walkway and steppedover an obstacle. The volunteers were instructed to walk upright and step over the obstaclewith the right (leading) limb in the seventh step and the left (trailing) limb in the eighth
step. An obstacle was placed in the middle of the walkway. Before the recording session,
the volunteers were instructed to adjust the starting position without stepping over the
obstacle. We used rectangular and trapezoidal obstacles as illustrated in Figure 4-1. The
height of the rectangular obstacle was 15 cm. Since both the leading limb and trailinglimb were expected to cross the height of 15 cm, we referred to the rectangular obstacle
as L15-T15. In one group of the trapezoidal obstacles, the height at 10 cm to the right ofthe middle of the obstacle was fixed to 15 cm, and the height at 10 cm to the left of the
middle of the obstacle was set to 10, 12, 14, 16, 18, and 20 cm (Figure 4-1-B). We referredto these trapezoidal obstacles as L15-T10, L15-T12, L15-T14, L15-T16, L15-T18, andL15-T20, respectively. Similarly, we created another group of trapezoidal obstacles (L10T15, L12-T15, L14-T15, L16-T15, L18-T15, and L20-T15) of which the height at 10 cm
53

to the left was fixed to 15 cm, and the height at 10 cm to the right was set to 10, 12, 14,
16, 18, and 20 cm (Figure 4-1-C).

54

Figure 4-1. The geometry of the obstacles. A. A rectangular 150-mm-height obstacle witha flat top edge was used as a reference. B. Trapezoidal obstacles of which the height of
the leading limb was fixed at 150 mm. The height of the trailing limb was set from 100
55

mm to 200 mm. C. Trapezoidal obstacles of which the height of the trailing limb was
fixed at 150 mm.

The experiment was block-designed. The participants repeated ten trials for agiven obstacle session and then moved to another obstacle session. The order of thesession varied among the participants. Sessions 1, 8, and 15 were always the rectangularobstacle (15-15) sessions. For eight participants, sessions 2–7 were group B trapezoidal
obstacles (15–**), and sessions 9–14 were group C obstacles (**-15). For the other eightparticipants, the order of group B and C trapezoidal obstacles was opposite. Withinsessions 2–7 or 9–14, the order of the obstacles was randomized so that right-side-down
and left-side-down obstacles were alternated.

Data collection
Reflective markers were pasted on two anatomical landmarks on the left andright distal condyle of the first metatarsal bone. The markers were captured using a 3D
optical motion caption system (Qualisys Track Manager, Qualisys, Göteborg, Sweden)with eight cameras (Qualisys-Miqus M3, Qualisys). The sampling frequency of thekinematic data was 250 Hz. The measured signals were stored on a computer, and all56

numerical calculations were performed using MATLAB 2017b (Math Works, Inc., MA,
USA).

Data analysis
In this study, participants were not asked to practice crossing over before theexperiment. Therefore, the first ten trials in which participants traversed a rectangularobstacle were excluded from the analysis. In addition, the left leg was the leading limb in
two trials. The left toe marker could not be measured because it could not be captured by
the camera in two trials. The participants contacted the obstacle in ten trials. These trials
were excluded from the analysis. The kinematic data were low-pass filtered using a zerolag second-order Butterworth digital filter with a cutoff frequency of 10 Hz. The limb
trajectory during obstacle crossing was quantified for the leading and trailing limbs using
the following parameters (Figure 4-2). The vertical MP1 position was defined as being
measured from the floor. The mediolateral MP1 position was in the mediolateral direction
with the center of the obstacle as the origin. The MP1 radial clearance was the shortest
distance from the obstacle to the MP1 marker and the MP5 radial clearance was theshortest distance from the obstacle to the MP5 marker.

57

Figure 4-2. Illustration of radial foot clearances in the frontal plane. The foot clearanceswere calculated based on MP1 (black circle) and MP5 (black square) markers.

Statistics
For all the dependent variables, we used one-way repeated-measures ANOVA toinvestigate the effect of the obstacle’s shape on the foot trajectory of the lower limb.
Bonferroni correction was used for the post hoc comparisons. If a violation of sphericity
was determined using Mauchly’s Test, Greenhouse–Geisser correction was performed.
The significance was set a priori at p < 0.05. Statistical analyses were performed using
JASP version 0.16.1.0 (Eric-Jan Wagenmakers, Amsterdam, Netherlands).

Results
In this study, the lower limb movements during the traversal of an obstacle were58

controlled not only in the vertical direction but also in the mediolateral direction bycontrolling the foot trajectory to reduce the risk of contact. The results for the vertical
MP1 position, mediolateral MP1 position, and MP1 and MP5 radial clearance arepresented in the following section.
Repeated measures ANOVA tests revealed the significant influential effects of
the obstacle conditions on the vertical MP1 position in the leading and trailing limbs.
(leading limb: F (2.804,42.065) = 3.823, p = 0.018, η2 = 0.203; trailing limb: F (6, 90) = 6.363,
p < .001, η2 = 0.298). Based on the post hoc test, the vertical MP1 position of the leading
limb in the L15-T10 and L15-T12 was larger compared to that of the rectangular obstacle(i.e., L15-T15). (L15-T10 :t (15) = 3.669, p < 0.0083, Cohen’s d = 0.374; L15-T12 : t(15) = 3.38, p < 0.0083, Cohen’s d = 0.345) (Figure 4-3-B). The vertical MP1 positionof the trailing limb in the L10-T15 was larger than that of the rectangular obstacle (L10T15: t (15) = 5.377, p < 0.0083, Cohen’s d = 0.672) (Figure 4-3-D).
Significant influential effects of the obstacle conditions on the mediolateral MP1
position were observed for the leading and trailing limbs (leading limb: F (2.436, 36.535) =18.244, p < .001, η2 = 0.549; trailing limb: F (1.866, 27.997) = 20.301, p < .001, η2 = 0.575).
There were significant differences between L15-T12 and L15-T15, between L15-T20 and
L15-T15 in the leading limb (L15-T12: t (15) = -3.341, p < 0.0083, Cohen’s d = -0.591;
59L15-T20: t (15) = -4.814, p < 0.0083, Cohen’s d = -0.852) (Figure 4-3-B). There weresignificant differences between L10-T15 and L15-T15, between L12-T15 and L15-T15,
and between L20-T15 and L15-T15 in the trailing limb (L10-T15: t(15) = 4.554, p <0.0083, Cohen’s d = 0.683; L12-T15: t(15) = 3.767, p < 0.0083, Cohen’s d = 0.565; L20T15: t(15) = 3.467, p < 0.0083, Cohen’s d = 0.52) (Figure 4-3-D). These results indicatethat both the leading and trailing limbs were consistently displaced in the direction of thelow height of the obstacle during the crossing of the trapezoidal obstacles.

Figure 4-3. The vertical and mediolateral MP1 position of the leading limb (A, B) andtrailing limb (C, D). In the left panels, the mean MP1 positions for all the obstacle
60

conditions are shown. To visualize the foot position relative to the obstacle, threeobstacles (15-10, 15-15, and 15-20 in panel A; 10-15, 15-15, and 20-15 in panel C) areillustrated in panels A and C. The right panels show the mean and standard deviations of
the foot position (B, D). The asterisks and hash marks indicate significant differences forthe rectangular 15-15 obstacles in the vertical and mediolateral MP1 positions,
respectively. The significance level was adjusted to p < 0.0083 (0.05/6) based on the
Bonferroni correction.

Significant influential effects of the obstacle’s conditions on the MP1 radial
clearance were observed in the leading and trailing limbs (leading limb: F (6, 90) = 21.948,
p < .001, η2 = 0.594; trailing limb: F (6, 90) = 15.607, p < .001, η2 = 0.510). A significantly
larger MP1 radial clearance was observed in the L15-T10, L15-T12, and L15-T14
compared to that of the rectangular obstacle in the leading limb (L15-T10: t(15) = 8.248,
p < 0.0083, Cohen’s d = 0.808; L15-T12: t(15) = 6.61, p < 0.0083, Cohen’s d = 0.648;
L15-T14: t(15) = 4.45, p < 0.0083, Cohen’s d = 0.436) (Figure 4-4-A), and L10-T15,
L12-T15 and L14-T15 compared to that of the rectangular obstacle in the trailing limb
(L10-T15: t(15) = 7.843, p < 0.0083, Cohen’s d = 0.961; L12-T15: t(15) = 4.6, p <0.0083, Cohen’s d = 0.564; L14-T15: t(15) = 3.64, p < 0.0083, Cohen’s d = 0.446)
61

(Figure 4-4-B).
There was a significant influential effect of the obstacle conditions on the MP5radial clearance in the leading and trailing limbs (leading limb: F (6, 90) = 7.259, p < .001,
η2 =0.326; trailing limb: F (6, 90) = 4.071, p = 0.001, η2 = 0.213). A significantly larger
MP5 radial clearance was observed in the L15-T18 and L15-T20 compared to that of therectangular obstacle in the leading limb (L15-T18: t(15) = -3.977, p < 0.0083, Cohen’s d= -0.437; L15-T20: t(15) = -6.261, p < 0.0083, Cohen’s d = -0.688) (Figure 4-4-A). A
significantly larger MP5 radial clearance was observed in the L10-T15 and L16-T15
compared to that of the rectangular obstacle in the trailing limb (L10-T15: t(15) = 4.508,
p < 0.0083, Cohen’s d = 0.58; L16-T15: t(15) = -3.931, p < 0.0083, Cohen’s d = -0.505)(Figure 4-4-B).

Figure 4-4. The MP1 and MP5 radial clearance of the leading limb (A) and trailing limb
62

(B). The mean and the 95% confidence intervals are illustrated. The daggers indicate
significant differences for the rectangular obstacle (150 mm condition) in MP1 radial
clearance with p < 0.0083 (0.05/6). The section describes the significant differences forthe rectangular obstacle (150 mm condition) in the case of MP5 radial clearance with p <0.0083 (0.05/6).

Discussion
We intended to investigate whether the mediolateral foot position was taskinfluenced during obstacle crossing. In the investigation, the foot trajectory during thecrossing of trapezoidal obstacles was measured. The hypothesis was confirmed based on
the results that if the obstacle was left-up-right-down, the foot was moved rightward
compared to the flat obstacle condition and vice versa for the right-up-left-down obstacles.
The amplitude of the mediolateral MP1 position was linearly related to the tilt angle ofthe obstacle. The foot trajectory for obstacle crossing was determined by considering thetradeoff between energy minimization and the minimization of the risk of contact withobstacles [12]. The physiological energy increases in proportion to the lifting height in
obstacle-crossing [77]. Although no studies have quantitatively estimated the energy
expenditure associated with the mediolateral MP1 position during obstacle traversal, it is63possible that at least for our healthy young participants, the mediolateral MP1 position
might be more efficient than vertically lifting the foot to ensure foot clearance. The
observed mediolateral movement of the foot might be regarded as a strategy for securing
clearance when traversing trapezoidal obstacles.
For the leading limb, a significantly larger MP1 radial clearance was observed
when the participants crossed the L15-T10, L15-T12, and L15-T14 trapezoidal obstacles
compared to the 15-cm-high rectangular obstacle. For these obstacles, the lateral side washigher than the medial side resulting in an increased risk of contact of the lateral side of
the foot with the obstacles. For these obstacle conditions, the radial clearance that wasdetermined using the MP5 marker was not significantly different from the rectangularobstacle condition. Conversely, the MP1 radial clearance for the L15-T16, L15-T18, andL15-T20 obstacles was not significantly different from that of the rectangular obstacle,
whereas the MP5 radial clearance for the L15-T18 and L15-T20 obstacles was larger
compared to that of the rectangular obstacle. Overall, the smaller value for the radial
clearances of MP1 and MP5 in any trapezoidal obstacle was not statistically different
from the foot clearance in the rectangular obstacle. A similar result was also confirmed
for the trailing limb. These findings suggest that the participants-maintained footclearance and the risk of collision of both the medial and lateral sides of the foot with the64

obstacles.
As previously indicated, the foot clearance for the trapezoidal obstacles was not
significantly different from that for the rectangular obstacle. The only exception was the
L10-T15 condition where both the MP1 and MP5 radial clearances for the trailing limb
were larger compared to that of the reference foot clearance for the rectangular obstacle.
The traversal of obstacles while walking is dependent on the visual information stored in
the brain [4]. The position of the trailing limb relative to an obstacle cannot be confirmed
using online visual information. This means that the control of the trailing limb is more
uncertain compared to the leading limb. Previous studies have reported an increase in footclearance in the case of high uncertainty, such as when the subject’s gaze was averted
from the stair for 2 seconds or more [13]. In the L10-T15 condition, the obstacle’s height
was higher on the lateral side of the trailing limb, where the risk of collision could behigher for the lateral side of the foot. A previous psychological study demonstrated thathumans tend to misjudge their foot position as being more medial compared to their actual
foot position and the authors suggested that this discrepancy might lead to unexpected
tripping during walking [22]. If the perception of the location of the lateral side of thefoot is uncertain, the results indicate that the participants increase foot clearance when therisk of tripping is considered as a security strategy for adaptive locomotion.
65

Although the result of the present study was qualitatively reasonable, it might bepremature to conclude that it is optimal in a quantitative sense. The basic principle ofmotor control is energy minimization [12]. If it applies to our experimental results, theobserved mediolateral MP1 position can be regarded as an energy-efficient strategy toensure foot clearance compared to the vertical MP1 position, which guarantees the sameclearance. For the shallowest conditions, the slope of the top edge of the obstacle wasonly 5% (i.e., 1 cm vertical difference for 20 cm width). For such obstacles, we observed
approximately 1 cm mediolateral displacement, which contributes to an increase of theclearance by 0.5 mm. In these cases, the energy cost of moving the foot 1 cm along a
mediolateral trajectory should be comparable to that associated with vertically lifting thefoot by 0.5 mm. When we examined the steepest condition for which the slope was 25%,
the observed mediolateral MP1 positions were 2–3 cm. The proportion of the observed
mediolateral MP1 position and the slope was not linear for the various tested slopes.
Detailed computational studies are required to determine whether the observed
mediolateral displacements are quantitatively equivalent in terms of securing footclearance.
It is known that human decision-making might be suboptimal in economic,
perceptual, and motor tasks [80,81]. Ota and his colleagues reported on persistent66

suboptimality in decision-making when the cost function was asymmetric for the giventask [82–84]. In his study, the subjects were rewarded as their performance improved to
be close to the target. However, zero rewards were given if the performance exceeded thetarget. They considered that the non-linearity of the cost function might be a challenge interms of calculating the optimal solution. Obstacle-crossing tasks have a similar costfunction wherein the physiological cost gradually decreases as the clearance becomesclose to zero. However, a high cost would be associated with tripping if the clearance isnegative. Although we did not test the optimality of the obstacle-crossing behavior, it
should be noted that the non-linearity of the cost function in obstacle-crossing tasks may
limit the motor control system in terms of quantitatively calculating the optimal obstaclecrossing behavior.
It would be interesting to investigate the foot trajectory in the frontal plane ofelderly people, amputees, and patients diagnosed with stroke or Parkinson’s disease. For
these populations, it can be assumed that the motor cost of lifting the foot was higher, thebalance-maintaining ability was lower, the result of the tripping was more serious, andperception and memory-related functions were impaired compared to healthy young
people [26,51,85]. Crossing a trapezoidal obstacle is a complex task that requires theintegration of these functions. Ambulatory obstacle-crossing has been reported to be67

different in patients with Parkinson's disease compared to healthy individuals, withincreased asymmetry in the left and right legs [51] and greater clearance in stroke patients[86]. These findings suggest that the behavior of trapezoidal obstacle crossing in otherpopulations (e.g., osteoarthritis patients, hemiplegic patients, and individuals with othermusculoskeletal and neurological disorders) may differ compared to healthy subjects. In
future research, the crossing over-straddle behavior in other populations with different
locomotor costs for healthy individuals to determine how the disease may affect obstacle
crossing in complex environments.

Conclusions
In this study, we observed that the leading limb moved the foot to the left when
the obstacle shape was upper right and lower left, and conversely, moved the foot to theright when the obstacle shape was lower right and upper left. The same behavior wasobserved in the trailing limb as in the leading limb. These results suggest that themediolateral position of the feet when crossing over obstacles is influenced by the shapeof the obstacle. In addition, in the leading limb radial clearance, MP5 radial clearance
maintained the same clearance as a rectangular obstacle when the shape was upper rightand lower left. Conversely, when the obstacle’s shape was lower right and upper left, the68MP1 radial clearance maintained the same clearance as a rectangular obstacle. The same
behavior was generally observed in the trailing limb. These results suggest that theparticipants-maintained foot clearance and both the medial and lateral sides of the footwere at risk of collision with the obstacle.

Funding
This work was supported by the following grants. MEXT KAKENHI Grant-inAid, Grant Number: 21H05334. Tateisi Science and Technology Foundation. JSTSPRING, Grant Number JPMJSP2132.

69

Chapter 5.
General Discussion
Abstract
The objective of this study was to determine whether the trajectory of the footduring obstacle crossing is differentially controlled by the shape of the obstacle. The main
findings are as follows: (1) There was an interaction in the motor control between theleading and trailing limbs, and the height of the obstacle crossed by the opposite leg andthe motion of the opposite leg affected the motor control of the lower limb during thetraversal of the obstacle. (2) When crossing an irregularly shaped obstacle, the motion of
the lower limb was controlled not only in the vertical direction but also in the lateral
direction, considering the shape of the obstacle. (3) This implies that even a healthy
person may perform irrational crossing-over movements. (4) The motion of the lower
limb in crossing obstacles is not determined by the height of the obstacle directly under
the foot but by the shape of the entire obstacle, including the opposite limb.
In the study of obstacle traversal, the findings suggest not only that the motor
control of the lower limbs is independent, but also a new theory that the left and right legs
are controlled by mutual motor influences. It is also proposed that motor control of thelower limb during the traversal of obstacles may be prioritized using a strategy of leftright foot control rather than foot elevation over the obstacle. In addition, quantitative as
well as qualitative evaluation of the lower limb may allow for a more detailed evaluationof the motor control of this limb during the crossing of an obstacle.
Finally, this study elucidates the control of obstacle traversal in complex
environments, similar to typical circumstances. It is expected that the findings of thisstudy will facilitate a better understanding of the mechanism of falls associated withcontact with obstacles, and more effectively address the social problem of accidental falls
among the elderly, to minimize their occurrence.

70

Chapter 5.
General Discussion
Abstract (in Japanese)
本研究の目的は，障害物横断時の足の軌跡が障害物の形状によって異なる制御がされるかどうかを明らかにすることであった。本研究で得られた知見は、(1) 左右脚間の運動制御には相互作用が存在し、反対脚が跨いだ障害物の高さや、反対脚の運動が障害物跨ぎ越し歩行時の下肢の運動制御に影響を与える。(2) 不定形な障害物を跨ぐ際には、下肢の運動は鉛直方向だけではなく左右方向の制御も含めた、障害物全体の形状も考慮に入れて制御しているということである。(3) 健常者であっても非合理的な跨ぎ越し運動を行う可能性を示唆した。(4) 障害物越えの歩行における下肢の運動は、足の真下にある障害物の高さ
ではなく、反対側の肢を含む障害物全体の形状によって決まるということである。
障害物跨ぎ越し歩行分野において、本研究から得られた知見は、「下肢の運動制御は独立している」という説だけではなく、「左右脚は相互に運動の影響を受けて制御がなされている」という新たな説を示唆するものである。また、障害物跨ぎ越し歩行における下肢の運動制御は、障害物の形状に応じて足部の挙上よりも、左右方向の足部の制御を行う戦略が優先される可能性を提唱する。加えて、定性的な下肢の評価だけではなく、定量的な評価を行うことで、より詳細に障害物跨ぎ越し歩行における、下肢の運動制御を評価できる可能性がある。
最後に、本研究は日常生活に近いより複雑な環境下での障害物跨ぎ越し歩行制御を明らかにした研究である。本研究で得られた知見は、障害物の接触による転倒機序の解明の一助となり、社会問題である高齢者の転倒問題の解
決と、転倒予防方法の考案に繋がることが期待される。

71

1. Objectives and results of this study
The objective of this study was to determine whether the trajectory of the foot is
influenced by the shape of an obstacle during its traversal. In Chapter 3, experiments were
performed to compare the foot trajectories for the crossing of obstacles of different
heights on the left and right sides, and the crossing of an obstacle of the same height on
the left and right sides. It was determined that the foot trajectory when crossing an
obstacle was affected not only by the height of the obstacle but also by the motion of the
opposite leg and the height of the obstacle that the opposite leg crossed. In Chapter 4, forthe tasks of crossing a trapezoidal obstacle and a rectangular obstacle, we established thatthe foot controls the lower limb not only in the vertical direction but also in the lateral
direction, considering the shape of the entire obstacle. It was also determined that even
healthy people may perform irrational locomotion. Based on the two experiments, it isevident that the motion of the lower limb during the crossing of an obstacle is notdetermined by the height of the obstacle directly under the foot, but by the shape of theentire obstacle, including the opposite limbs. In this chapter, we discuss the significanceof the findings in Chapters 3 and 4 considering gait control and its anticipated contribution
to human health.

72

2. Explanation of similarities and differences between Chapters 3 and 4
Chapter 3 presented the results for a task involving obstacles of different heights
for traversal by the leading and trailing limbs. In Chapter 4, unlike Chapter 3, theobstacles to be traversed by the leading and trailing limbs were not set separately. Instead,a single trapezoid-shaped obstacle was crossed by the leading and trailing limbs. In thecase of Chapter 4, the obstacles were crossed using not only vertical, but also lateral footcontrol, although the opposite leg was affected by the obstacle crossed and the motion of
the opposite leg, and the foot was elevated. However, from a quantitative perspective, theparticipants performed lateral movements although the movement of the foot by 1 cm inthe lateral direction only resulted in a height of 0.5 mm in the vertical direction,suggesting that the participants potentially performed irrational movements. The
differences between the two studies are as follows: (1) The shape of the obstacle that wascrossed was different, i.e., whether it was an obstacle divided into left and right sections
or a trapezoidal obstacle combined to yield left and right sections; (2) When the shape ofthe obstacle was different, it was observed that the foot controlled not only vertical but
also lateral movement. (3) It was observed that even healthy adults performed irrational
movements. The findings from the two experiments indicate that the motion of the lower
limb during the crossing of an obstacle is not determined by the height of the obstacle
73directly under the foot, but by the shape of the entire obstacle, including the opposite
limbs.

3.

Contribution to the field of gait control
The main findings are as follows: (1) There was an interaction in the motor

control between the leading and trailing limbs, and the height of the obstacle crossed by
the opposite leg and the motion of the opposite leg affected the motor control of the lower
limb during the traversal of the obstacle. (2) When crossing an irregularly shaped obstacle,
the motion of the lower limb was controlled not only in the vertical direction but also in
the lateral direction, considering the shape of the obstacle. (3) This implies that even ahealthy person may perform the irrational crossing-over motion. (4) The motion of thelower limb during the crossing of obstacles is not determined by the height of the obstacle
directly under the foot, but by the shape of the entire obstacle, including the opposite limb.
The implications of each finding in the field of gait control are discussed below.
First, (1) "There was an interaction in the motor control between the leading andtrailing limbs. Moreover, the height of the obstacle crossed by the opposite leg and the
motion of the opposite leg affects the motor control of the lower limb during the crossingof an obstacle". Previous adaptive gait studies have shown that lower limb movements
74were independently controlled [14,15]. The main concept is that the motion and feedbackof one lower limb are not used to control the other. To adapt gait in various environments,
it is necessary to use a variety of sensory information, including visual information. The
three systems used to control walking locomotion are the visual, vestibular, andsomatosensory systems [87]. Among these, visual information is needed to understandthe surrounding environment. For example, if there is an obstacle in the walking path, theheight, shape, and location of the obstacle must be visually assessed to make appropriate
choices such as whether to step over, go around, or through the obstacle. In addition, theheight, shape, and location of an obstacle obtained based on visual information are stored
as a form of short-term memory called working memory [13], which is used to control
the lower limbs. Humans can see obstacles when the leading leg moves over them, but
not when the trailing leg traverses them. Heijnen et al. [12,31] discovered that this absenceof visual feedback led to frequent obstacle contact with the trailing leg. They reported on
the possibility of using context, perception, and working memory to compensate for thislack of information. In addition, they determined that when an obstacle is not visible, thelower limb must be guided over the obstacle using stored visuospatial representations[13,31,88,89]. Considering these findings, previous obstacle-crossing gait studies
involved tasks in which the leading and trailing limbs crossed obstacles of the same height75

separately. In these investigations, the leading limb was the first limb to cross the obstacle
and the following leg was the trailing limb [10]. Clearance was used as a typical index
for evaluating lower limb motion in obstacle-crossing gait [10]. Clearance is the verticaldistance between the foot and the obstacle. From previous studies, the factors that alter
clearance include time constraints [25], aging [16], cognitive function [19], genderdifferences [18], obstacle height, and the depth of objects [9]. However, none of thesestudies focused on interactions in the motor control of the leading and trailing limbs.
Moreover, the role of factors in the motor control of the lower limb such as the motion of
the opposite leg and the height of the obstacle traversed by the opposite leg has not been
elucidated. The findings of this study suggest not only a theory of independent motor
control of the lower limb during the crossing of obstacles but also a new theory that thelower limb is influenced by the reciprocal motion of the leading and trailing limbs.
The finding that (2) when crossing an irregularly shaped obstacle, the lower
limb motion was controlled not only in the vertical direction but also in the lateral
direction is discussed considering the shape of the entire obstacle. In previous studies on
the crossing of obstacles, vertical clearance was evaluated as the risk of contact with the
obstacle [10]. To reduce this risk during overpass walking, one solution is to elevate thefoot. In obstacle-crossing gait, lower limb movements are controlled based on an energy
76minimization strategy [12], and clearance is determined based on a trade-off between
minimizing energy consumption and the risk of contact with the obstacle. However,Yamagata et al. (2021) [78] reported that the strategy of ensuring clearance by elevating
the foot is not always a safe method of crossing obstacles because excessive footelevation may lead to left-right instability. Thus, ensuring vertical clearance is notnecessarily a safe way to cross an obstacle. In addition, the vertical MP1 position of thefoot may have a greater energy cost compared to the case of lateral displacement.
Slawinski et al. (2014) [77] reported that energy expenditure increases with footelevation in healthy subjects. In addition, clearance during obstacle traversal decreases
with the number of trials, indicating that the motor control strategy of the lower limb isbased on an energy minimization strategy [12]. Thus, in this dissertation, it is proposedthat the lower limb motor control based on the crossing of obstacles may be prioritizedusing a strategy that controls the foot in the mediolateral direction. This is associatedwith a low energy cost and can safely allow for the traversal of obstacles, rather thanfoot elevation, which has a high energy cost and induces instability, depending on the
obstacle’s geometry.
Thirdly, (3) the possibility that even healthy individuals may engage inirrational crossing-over movements was suggested. Human economic activity may be77suboptimal because of limited information processing and limited computational power[90,91]. Irrespective of the type of exercise that is planned, the executed and planned
exercises do not necessarily coincide owing to variability in the exercise [92].
Therefore, it is necessary to consider one's motion variability to set an optimal motion
plan. However, Ota et al. (2019) [82] reported that motor planning in an upper limb
reaching task was not optimal, even when participants were explicitly provided withvisual feedback information on the variation of their movements from the target (motor
uncertainty). Ota et al. (2019) [82] suggested that this non-optimization of exercise
planning may be owing to limitations in our ability to use this information to perform
calculations while accounting for reward-risk tradeoffs, even if we have the informationneeded to optimize the exercise plan. From a quantitative perspective in terms of energy
consumption, it was not possible to determine whether crossing an obstacle with thefoot elevated 0.5 mm or crossing an obstacle with the foot moved 1cm to the left or
right would result in lower energy consumption. Moreover, no studies have beenreported that identify the case in which the energy consumption is smaller. However,based on the reports of Ota et al. [82] and Simon [90,91], it is possible that theparticipants in the study had restricted cognitive ability, and were unable to optimize
their exercise plans, resulting in irrational obstacle-crossing movements. Previous
78

obstacle-crossing gait studies have compared healthy young adults and elderly subjects[16] and those at high and low risk of falling [27]. These studies evaluated obstacle
contact risk in terms of the vertical clearance required to cross an obstacle, and only
considered qualitative measures, such as the effects of aging and fall risk on clearance.
This study examined the motor control of the lower limb during obstacle crossing indetail from a quantitative perspective. By conducting a quantitative evaluation of
movement during the crossing of the obstacles, the possibility of irrational movementthat cannot be detected based only on this approach was suggested.
Finally, (4) The motion of the lower limb during the crossing of obstacles is notdetermined by the height of the obstacle directly under the foot, but by the shape of theentire obstacle, including the opposite limb. In previous studies of obstacle-stepping
gait, it has been suggested that memory functions contribute to the control of the trailingleg [19] and that the neural resources of memory based on visual input between theleading and trailing legs are shared [32]. Therefore, it has also been suggested that upper
limb locomotion is under comprehensive motor control that includes the movement of
the opposite limb and the movements that were performed before and after the
movement [28–30]. These findings suggest that motor control of the lower limb in
obstacle crossing may contribute to motor memory and feed-forward control. Previous
79

studies have not focused on the interaction of movements between the left and rightlegs, and the influence of one leg on the other has not been clarified. When crossing
over obstacles of different heights, both the leading and trailing legs need to control the
lower limbs using motor memory and feed-forward control. The obstacles used in thepast in obstacle crossing studies, which included hurdles and boxes, were rectangularwith uniform heights on both sides. Thus, the effect of the height of the obstacle on the
opposite leg's lower limb movement was not considered [10]. This investigation is thefirst known report on overpass gait using obstacles with different heights on the left andright sides. The results suggest that the motion of the lower limb during overpass is notdetermined by the height of the obstacle directly under the foot, but also by the motionof the opposite leg, the height of the obstacle to be crossed by the opposite leg, and theshape of the obstacle.

4.

Solving the fall problem
Accidental falls in the elderly are more likely to result in sequelae such as

fractures and bedridden patients compared to younger individuals, which can negatively
impact health, independence, and quality of life [57]. It has been shown that the risk offalls is higher in women than in men, regardless of age [93,94]. Therefore, this problem
80

represents an urgent social issue that must be addressed, and not only for the elderly. To
minimize the occurrence of falls and improve the quality of life of patients, it is necessary
to elucidate the underlying mechanisms.
The results of this study showed that motor control between the leading andtrailing limbs during the crossing of an irregularly shaped obstacle is affected by theheight and motion of the obstacle in the case of the opposite leg. Previous obstaclecrossing studies used obstacles of the same height for the left and right sides [10].
However, typical obstacles do not always have symmetrical and regular shapes. Therefore,
it is necessary to conduct studies involving the traversal of obstacles in an environmentthat is more similar to the real world. In this study, a new experimental paradigm, thecrossing of irregularly shaped obstacles, was investigated. This approach has not beenused in previous studies on obstacle crossing. To safely step over an irregularly shaped
obstacle, it is necessary to assess its shape and height based on visual information and tocontrol the foot trajectory based on this data. When crossing obstacles of the same height
on both sides, it is sufficient to raise the feet to the same height on both sides, which is arelatively simpler control when crossing regularly shaped obstacles. However, during thetraversal of an irregularly shaped obstacle, the vertical and lateral distances between thefoot and the obstacle differ depending on the position of the foot. Therefore,81comprehensive control that includes not only the height of the obstacle directly under thefoot but also the shape of the entire obstacle is necessary to avoid contact with it. The
findings presented in this study allow for a deeper understanding of control during
obstacle traversal in complex environments that are similar to that typical scenarios andis an important step in the elucidation of the mechanism of falls owing to contact withobstacles, as well as the prevention of falls in the elderly.

5.

Limitations
The limitations of this study are that (1) the subjects were healthy young adults.

Previous studies on obstacle traversal involved patients with Parkinson's disease [51,95],
the elderly [16,19,26,27,96], and patients who suffered a stroke [85,97–99]. To devise amethod to prevent falls owing to contact with obstacles while traversing them, it isnecessary to conduct research not only on healthy young adults but also on subjects withdifferent diseases and different age groups and to investigate the characteristics of eachsubject's lower limb movements by comparing the movements of each group. (2) In thisinvestigation, only clearance was calculated, which means that the consideration of theresults that the motion of the opposite leg and the height of the obstacle crossed by the
opposite leg affected the clearance of the ipsilateral leg may be due to motor memory or82feed-forward control is left to speculation. The clearance of both the leading and trailinglegs was affected by the height of the obstacle that the opposite leg straddled and the
motion of the opposite leg. Although the results suggest the existence of an interaction
between the two legs, the factor that caused the greater clearance of the leading leg could
not be explained by the interaction, suggesting the possibility of predictive motor control.
Findings, such as the report that memory function has been shown to contribute to thecontrol of the trailing leg in obstacle-stepping gait [19], the suggestion of shared neural
resources of memory based on visual input between the leading and trailing limbs [32],and that upper limb movements, may be related to that of the opposite limb It has beensuggested that upper limb movements may be under comprehensive motor control that
includes the movements of the opposite limb and the type of movements that were
performed before and after the movement [28–30]. These findings suggest that motor
control of the lower limb during obstacle crossing may contribute to motor memory andfeed-forward control. To confirm the existence of motor control interactions between theleft and right legs, it is necessary to elucidate the relationship between memory function
and feed-forward control mechanisms in obstacle-crossing gait.

83

Reference[1]

B. Senut, M. Pickford, D. Gommery, P. Mein, K. Cheboi, Y. Coppens, Firsthominid from the Miocene (Lukeino Formation, Kenya)., Comptes Rendus
l’Academie Des Sci. Ser. 2A Sci. La Terre Des Planetes. 332 (2001) 137–144.

[2]

M.D. Sockol, D.A. Raichlen, H. Pontzer, Chimpanzee locomotor energetics andthe origin of human bipedalism, Proc. Natl. Acad. Sci. U. S. A. 104 (2007)
12265–12269. https://doi.org/10.1073/PNAS.0703267104.

[3]

C. Owen Lovejoy, G. Suwa, L. Spurlock, B. Asfaw, T.D. White, The pelvis andfemur of ardipithecus ramidus: The emergence of upright walking, Science(80-. ). 326 (2009). https://doi.org/10.1126/SCIENCE.1175831.

[4]

A.E. Patla, S.D. Prentice, C. Robinson, J. Neufeld, Visual Control of
Locomotion: Strategies for Changing Direction and for Going Over Obstacles, J.
Exp. Psychol. Hum. Percept. Perform. 17 (1991) 603–634.
https://doi.org/10.1037/0096-1523.17.3.603.

[5]

R. Moraes, M.A. Lewis, A.E. Patla, Strategies and determinants for selection ofalternate foot placement during human locomotion: influence of spatial andtemporal constraints, Exp. Brain Res. 159 (2004) 1–13.
https://doi.org/10.1007/S00221-004-1888-Z.
84

[6]

Aftad E. Patla, How Is Human Gait Controlled by Vision?, (1998) 287–302.

[7]

D.B. Elliot, A. Vale, D. Whitaker, J.G. Buckley, Does my step look big in this? A
visual illusion leads to safer stepping behaviour, PLoS One. 4 (2009) 2–7.
https://doi.org/10.1371/journal.pone.0004577.

[8]

Richard J. Foster, John G. Buckley, David Whitaker, David B. Elliott, The
addition of stripes (a version of the ‘horizontal-vertical illusion’) increases footclearance when crossing low-height obstacles, Ergonomics. 59 (2015) 884–889.
https://doi.org/10.1080/00140139.2015.1105304.

[9]A. Patla, S. Rietdyk, Visual control of limb trajectory over obstacles duringlocomotion: effect of obstacle height and width, Gait Posture. 1 (1993) 45–60.
https://doi.org/10.1016/0966-6362(93)90042-Y.

[10] B. Galna, A. Peters, A.T. Murphy, M.E. Morris, Obstacle crossing deficits inolder adults: A systematic review, Gait Posture. 30 (2009) 270–275.
https://doi.org/10.1016/j.gaitpost.2009.05.022.
[11] G.C. Avery, R.H. Day, Basis of the horizontal-vertical illusion, J. Exp. Psychol.
81 (1969) 376–380.
[12] M.J.H. Heijnen, B.C. Muir, S. Rietdyk, Factors leading to obstacle contact during
adaptive locomotion, Exp. Brain Res. 223 (2012) 219–231.
85https://doi.org/10.1007/s00221-012-3253-y.
[13] M. Shinya, A. Popescu, C. Marchak, B. Maraj, K. Pearson, Enhancing memoryof stair height by the motor experience of stepping, Exp. Brain Res. 223 (2012)
405–414. https://doi.org/10.1007/s00221-012-3269-3.
[14] S. Anstis, Aftereffects from jogging, Exp Brain Res. 103 (1995).
[15] S. Rietdyk, C.K. Rhea, The effect of the visual characteristics of obstacles on riskof tripping and gait parameters during locomotion, Ophthalmic Physiol. Opt. 31(2011) 302–310. https://doi.org/10.1111/J.1475-1313.2011.00837.X.
[16] B.C. Muir, J.M. Haddad, R.E.A. van Emmerik, S. Rietdyk, Changes in thecontrol of obstacle crossing in middle age become evident as gait task difficultyincreases, Gait Posture. 70 (2019) 254–259.
https://doi.org/10.1016/j.gaitpost.2019.01.035.
[17] R. Sakurai, M. Montero-Odasso, H. Suzuki, S. Ogawa, Y. Fujiwara, Motor
imagery deficits in high-functioning older adults and its impact on fear of fallingand falls, Journals Gerontol. - Ser. A Biol. Sci. Med. Sci. 76 (2021) E228–E234.
https://doi.org/10.1093/gerona/glab073.
[18] T.E. Raffegeau, G.K. Kellaher, M.J. Terza, J.A. Roper, L.J. Altmann, C.J. Hass,
Older women take shorter steps during backwards walking and obstacle crossing,86Exp. Gerontol. 122 (2019) 60–66. https://doi.org/10.1016/j.exger.2019.04.011.
[19] R. Sakurai, K. Kodama, Y. Ozawa, F. Pieruccini-Faria, K.E. Kobayashi-Cuya, S.
Ogawa, Association of age-related cognitive and obstacle avoidance
performances, Sci. Rep. 11 (2021) 1–9. https://doi.org/10.1038/s41598-02191841-9.
[20] I. Maidan, S. Eyal, I. Kurz, N. Geffen, E. Gazit, L. Ravid, N. Giladi, A.
Mirelman, J.M. Hausdorff, Age-associated changes in obstacle negotiation
strategies: Does size and timing matter?, Gait Posture. 59 (2018) 242–247.
https://doi.org/10.1016/J.GAITPOST.2017.10.023.
[21] N.M. Rinaldi, J. Lim, J. Hamill, R. Van Emmerik, R. Moraes, Walking combinedwith reach-to-grasp while crossing obstacles at different distances, Gait Posture.
65 (2018) 1–7. https://doi.org/10.1016/J.GAITPOST.2018.06.167.
[22] C. Szu-Hua, L. On-Yee, K. Taylor, C. Li-Shan, Concurrent phone texting alters
crossing behavior and induces gait imbalance during obstacle crossing, Gait
Posture. 62 (2018) 422–425. https://doi.org/10.1016/J.GAITPOST.2018.04.004.
[23] S. Kim, M.A. Nussbaum, S. Ulman, Impacts of using a head-worn display on gait
performance during level walking and obstacle crossing, J. Electromyogr.
Kinesiol. 39 (2018) 142–148. https://doi.org/10.1016/J.JELEKIN.2018.02.007.
87

[24] K.W. Wu, J. Da Li, H.P. Huang, Y.H. Liu, T.M. Wang, Y.T. Ho, T.W. Lu,
Bilateral asymmetry in kinematic strategies for obstacle-crossing in adolescentswith severe idiopathic thoracic scoliosis, Gait Posture. 71 (2019) 211–218.
https://doi.org/10.1016/j.gaitpost.2019.05.007.
[25] H. Chen, J.A. Ashton-miller, N.B. Alexander, A.B. Schultz, Effects of age andavailable response time on ability to step over an obstacle, J. Gerontol. Med. Sci.
49 (1994) 227–233. https://doi.org/10.1093/GERONJ/49.5.M227.
[26] R. Sakurai, Y. Fujiwara, M. Ishihara, T. Higuchi, H. Uchida, K. Imanaka, Agerelated self-overestimation of step-over ability in healthy older adults and its
relationship to fall risk, BMC Geriatr. 13 (2013). https://doi.org/10.1186/14712318-13-44.
[27] H.F. Pan, H.C. Hsu, W.N. Chang, J.H. Renn, H.W. Wu, Strategies for obstacle
crossing in older adults with high and low risk of falling, J. Phys. Ther. Sci. 28(2016) 1614–1620. https://doi.org/10.1589/jpts.28.1614.
[28] D. Nozaki, I. Kurtzer, S.H. Scott, Limited transfer of learning between unimanualand bimanual skills within the same limb, Nat. Neurosci. 9 (2006) 1364–1366.
https://doi.org/10.1038/nn1785.
[29] I.S. Howard, D.M. Wolpert, D.W. Franklin, The value of the follow-through88derives from motor learning depending on future actions, Curr. Biol. 25 (2015)
397–401. https://doi.org/10.1016/j.cub.2014.12.037.
[30] I.S. Howard, C. Ford, A. Cangelosi, D.W. Franklin, Active lead-in variability
affects motor memory formation and slows motor learning, Sci. Rep. 7 (2017) 1–
12. https://doi.org/10.1038/s41598-017-05697-z.
[31] M.J.H. Heijnen, N.L. Romine, D.M. Stumpf, S. Rietdyk, Memory-guided
obstacle crossing: More failures were observed for the trail limb versus lead limb,
Exp. Brain Res. 232 (2014) 2131–2142. https://doi.org/10.1007/s00221-0143903-3.
[32] S. Hagio, M. Kouzaki, Visuomotor transformation for the lead leg affects trail leg
trajectories during visually guided crossing over a virtual obstacle in humans,
Front. Neurosci. 14 (2020) 357. https://doi.org/10.3389/fnins.2020.00357.
[33] Y. Sekiguchi, K. Honda, S.-I. Izumi, Effect of walking adaptability on an unevensurface by a stepping pattern on walking activity after stroke, Front. Hum.
Neurosci. 15 (2022) 746. https://doi.org/10.3389/FNHUM.2021.762223.
[34] A.R. Oates, A.E. Patla, J.S. Frank, M.A. Greig, Control of dynamic stability
during gait termination on a slippery surface, J. Neurophysiol. 93 (2005) 64–70.
https://doi.org/10.1152/JN.00423.2004/ASSET/IMAGES/LARGE/Z9K01204427
8980008.JPEG.
[35] D.J. Liss, H.D. Carey, S. Yakovenko, J.L. Allen, Young adults perceive small
disturbances to their walking balance even when distracted, Gait Posture. 91(2022) 198–204. https://doi.org/10.1016/J.GAITPOST.2021.10.019.
[36] C.S. Baker, M.E. Cinelli, The effects of obstacle proximity on aperture crossing
behaviours, Exp. Brain Res. 235 (2017) 497–506.
https://doi.org/10.1007/s00221-016-4803-5.
[37] M.J.D. Caetano, S.R. Lord, D. Schoene, P.H.S. Pelicioni, D.L. Sturnieks, J.C.
Menant, Age-related changes in gait adaptability in response to unpredictableobstacles and stepping targets, Gait Posture. 46 (2016) 35–41.
https://doi.org/10.1016/j.gaitpost.2016.02.003.
[38] M.J.D. Caetano, J.C. Menant, D. Schoene, P.H.S. Pelicioni, D.L. Sturnieks, S.R.
Lord, Sensorimotor and cognitive predictors of impaired gait adaptability in older
people, J. Gerontol. A. Biol. Sci. Med. Sci. 72 (2017) 1257–1263.
https://doi.org/10.1093/gerona/glw171.
[39] M.J.D. Caetano, S.R. Lord, M.A. Brodie, D. Schoene, P.H.S. Pelicioni, D.L.
Sturnieks, J.C. Menant, Executive functioning, concern about falling andquadriceps strength mediate the relationship between impaired gait adaptability
90and fall risk in older people, Gait Posture. 59 (2018) 188–192.
https://doi.org/10.1016/j.gaitpost.2017.10.017.
[40] M.J.D. Caetano, S.R. Lord, N.E. Allen, J. Song, S.S. Paul, C.G. Canning, J.C.C.
Menant, Executive functioning, muscle power and reactive balance are major
contributors to gait adaptability in people with parkinson’s disease, Front. Aging
Neurosci. 11 (2019) 154. https://doi.org/10.3389/fnagi.2019.00154.
[41] L.A. Vallis, B.J. McFadyen, Children use different anticipatory control strategies
than adults to circumvent an obstacle in the travel path, Exp. Brain Res. 167(2005) 119–127. https://doi.org/10.1007/S00221-005-0054-6/TABLES/6.
[42] A.L. Hackney, M.E. Cinelli, Young and older adults use body-scaled information
during a non-confined aperture crossing task, Exp. Brain Res. 225 (2013) 419–
429. https://doi.org/10.1007/S00221-012-3382-3/FIGURES/5.
[43] H.-C. Chen, J.A. Ashton-Miller, N.B. Alexander, A.B. Schultz, Stepping overobstacles: Gait patterns of healthy young and old adults, Oxford Academic, 1991.
https://doi.org/10.1093/GERONJ/46.6.M196.
[44] A.E. Patla, E. Niechwiej, V. Racco, M.A. Goodale, Understanding thecontribution of binocular vision to the control of adaptive locomotion, Exp. Brain
Res. 142 (2002) 551–561. https://doi.org/10.1007/s00221-001-0948-x.
91

[45] J.S. Matthis, J.L. Yates, M.M. Hayhoe, C.B. Author, Gaze and the control of footplacement when walking in natural terrain HHS public access author manuscript,
Curr. Biol. 28 (2018) 1224–1233. https://doi.org/10.1016/j.cub.2018.03.008.
[46] D.A. McVea, K.G. Pearson, Long-lasting memories of obstacles guide leg
movements in the walking cat, J. Neurosci. 26 (2006) 1175–1178.
https://doi.org/10.1523/JNEUROSCI.4458-05.2006.
[47] D.A. McVea, A.J. Taylor, K.G. Pearson, Long-lasting working memories of
obstacles established by foreleg stepping in walking cats require area 5 of theposterior parietal cortex, J. Neurosci. 29 (2009) 9396–9404.
https://doi.org/10.1523/JNEUROSCI.0746-09.2009.
[48] A. Kim, N. Schweighofer, J.M. Finley, Locomotor skill acquisition in virtual
reality shows sustained transfer to the real world, J. Neuroeng. Rehabil. 16(2019) 113. https://doi.org/10.1186/s12984-019-0584-y.
[49] K. Binaee, G.J. Diaz, Assessment of an augmented reality apparatus for the studyof visually guided walking and obstacle crossing, Behav. Res. Methods. 51(2019) 523–531. https://doi.org/10.3758/s13428-018-1105-9.
[50] J. Krell, A.E. Patla, The influence of multiple obstacles in the travel path on
avoidance strategy, Gait Posture. 16 (2002) 15–19.
92https://doi.org/10.1016/S0966-6362(01)00194-1.
[51] D. Orcioli-Silva, F.A. Barbieri, P.C.R. dos Santos, V.S. Beretta, L. Simieli, R.
Vitorio, E. Lirani-Silva, L.T.B. Gobbi, Double obstacles increase gait asymmetry
during obstacle crossing in people with Parkinson’s disease and healthy older
adults: A pilot study, Sci. Rep. 10 (2020) 1–8. https://doi.org/10.1038/s41598020-59266-y.
[52] Z. Wang, J.H. Chien, K.C. Siu, Stepping over multiple obstacles changes thepattern of foot integrated pressure of the leading and trailing legs, J. Biomech. 98(2020) 109423. https://doi.org/10.1016/J.JBIOMECH.2019.109423.
[53] J.R. Berard, L.A. Vallis, Characteristics of single and double obstacle avoidance
strategies: A comparison between adults and children, Exp. Brain Res. 175(2006) 21–31. https://doi.org/10.1007/S00221-006-0529-0/FIGURES/5.
[54] M. Soma, H. Nakae, T. Abiko, R. Shimamura, H. Uematsu, K. Kawama,
Influence of a dual task while stepping over an obstacle in the fall-experienced
elderly people, J.Phys. Ther. Sci. 23 (2011) 369–372.
[55] D. Commandeur, M.D. Klimstra, S. MacDonald, K. Inouye, M. Cox, D. Chan,
S.R. Hundza, Difference scores between single-task and dual-task gait measures
are better than clinical measures for detection of fall-risk in community-dwelling93

older adults, Gait Posture. 66 (2018) 155–159.
https://doi.org/10.1016/j.gaitpost.2018.08.020.
[56] D.A. Jehu, D. Saunders, N. Richer, N. Paquet, Y. Lajoie, The influence of
carrying an anterior load on attention demand and obstacle clearance before,
during, and after obstacle crossing, Exp. Brain Res. 237 (2019) 3313–3319.
https://doi.org/10.1007/s00221-019-05673-1.
[57] A.J. Blake, K. Morgan, M.J. Bendall, H. Dallosso, S.B.J. Ebrahim, T.H.D. Arie,
P.H. Fentem, E.J. Bassey, Falls by elderly people at home: prevalence andassociated factors, Age Ageing. 17 (1988) 365–372.
https://doi.org/10.1093/ageing/17.6.365.
[58] H.J. Lipscomb, J.E. Glazner, J. Bondy, K. Guarini, D. Lezotte, Injuries from slips
and trips in construction, Appl. Ergon. 37 (2006) 267–274.
https://doi.org/10.1016/j.apergo.2005.07.008.
[59] P. Kannus, H. Sievänen, M. Palvanen, T. Järvinen, J. Parkkari, Prevention of falls
and consequent injuries in elderly people, Lancet. 366 (2005) 1885–1893.
https://doi.org/10.1016/S0140-6736(05)67604-0.
[60] M.E. Hahn, H.J. Lee, L.S. Chou, Increased muscular challenge in older adults
during obstructed gait, Gait Posture. 22 (2005) 356–361.
94https://doi.org/10.1016/j.gaitpost.2004.11.012.
[61] W.P. Berg, H.M. Alessio, E.M. Mills, C. Tong, Circumstances and consequencesof falls in independent community-dwelling older adults, Age Ageing. 26 (1997)
261–268. https://doi.org/10.1093/ageing/26.4.261.
[62] J.H. Chien, J. Post, K.C. Siu, Effects of aging on the obstacle negotiation strategy
while stepping over multiple obstacles, Sci. Rep. 8 (2018) 8576.
https://doi.org/10.1038/s41598-018-26807-5.
[63] G.P. Austin, G.E. Garrett, R.W. Bohannon, Kinematic analysis of obstacle
clearance during locomotion, Gait Posture. 10 (1999) 109–120.
https://doi.org/10.1016/S0966-6362(99)00022-3.
[64] H.L. Chen, T.W. Lu, Comparisons of the joint moments between leading andtrailing limb in young adults when stepping over obstacles, Gait Posture. 23(2006) 69–77. https://doi.org/10.1016/j.gaitpost.2004.12.001.
[65] N. van Melick, B.M. Meddeler, T.J. Hoogeboom, M.W.G. Nijhuis-van der
Sanden, R.E.H. van Cingel, How to determine leg dominance: The agreement
between self-reported and observed performance in healthy adults, PLoS One. 12(2017) e0189876. https://doi.org/10.1371/journal.pone.0189876.
[66] S. Cornus, G. Montagne, M. Laurent, Perception of a Stepping-Across95

Affordance, Ecol. Psychol. 11 (1999) 249–267.
https://doi.org/10.1207/s15326969eco1104_1.
[67] W.H. Warren, Perceiving affordances: Visual guidance of stair climbing., J. Exp.
Psychol. Hum. Percept. Perform. 10 (1984) 683–703.
https://doi.org/10.1037/0096-1523.10.5.683.
[68] K.G. Pearson, N. Arbabzada, R. Gramlich, M. Shinya, Leg mechanics contributeto establishing swing phase trajectories during memory-guided stepping
movements in walking cats: a computational analysis, Front. Comput. Neurosci.
9 (2015) 8. https://doi.org/10.3389/fncom.2015.00116.
[69] R. Sakurai, Y. Fujiwara, M. Yasunaga, H. Suzuki, Y. Murayama, K. Imanaka, K.
Kanosue, K. Ishii, Neural correlates of older adults’ self-overestimation of
stepping-over ability, Age (Omaha). 38 (2016) 351–361.
https://doi.org/10.1007/s11357-016-9932-z.
[70] R.P. Di Fabio, W.M. Kurszewski, E.E. Jorgenson, R.C. Kunz, Footlift
asymmetry during obstacle avoidance in high-risk elderly, J. Am. Geriatr. Soc.
52 (2004) 2088–2093. https://doi.org/10.1111/j.1532-5415.2004.52569.x.
[71] K. Pearson, R. Gramlich, Updating neural representations of objects during
walking, Ann. N. Y. Acad. Sci. 1198 (2010) 1–9. https://doi.org/10.1111/j.174996

6632.2009.05422.x.
[72] P. Kannus, H. Sievänen, M. Palvanen, T. Järvinen, J. Parkkari, Prevention of falls
and consequent injuries in elderly people, Lancet. 366 (2005) 1885–1893.
https://doi.org/10.1016/S0140-6736(05)67604-0.
[73] H.J. Lipscomb, J.E. Glazner, J. Bondy, K. Guarini, D. Lezotte, Injuries from slips
and trips in construction, Appl. Ergon. 37 (2006) 267–274.
https://doi.org/10.1016/j.apergo.2005.07.008.
[74] D. Muroi, S. Ohtera, Y. Kataoka, M. Banno, Y. Tsujimoto, H. Tsujimoto, T.
Higuchi, Obstacle avoidance training for individuals with stroke: A systematic
review and meta-analysis, BMJ Open. 9 (2019). https://doi.org/10.1136/bmjopen2018-028873.
[75] A.A. Mohagheghi, R. Moraes, A.E. Patla, The effects of distant and on-line
visual information on the control of approach phase and step over an obstacle
during locomotion, Exp. Brain Res. 155 (2004) 459–468.
https://doi.org/10.1007/s00221-003-1751-7.
[76] C.M. Said, M. Galea, N. Lythgo, Obstacle crossing following stroke improves
over one month when the unaffected limb leads, but not when the affected limb
leads, Gait Posture. 39 (2014) 213–217.
97https://doi.org/10.1016/j.gaitpost.2013.07.008.
[77] J. Slawinski, D. Pradon, D. Bensmail, N. Roche, R. Zory, Energy cost of obstacle
crossing in stroke patients, Am. J. Phys. Med. Rehabil. 93 (2014) 1044–1050.
https://doi.org/10.1097/PHM.0000000000000122.
[78] M. Yamagata, H. Tateuchi, T. Pataky, I. Shimizu, N. Ichihashi, Relation between
frontal plane center of mass position stability and foot elevation during obstacle
crossing, J. Biomech. 116 (2021) 110219.
https://doi.org/10.1016/J.JBIOMECH.2020.110219.
[79] Y. Miura, M. Shinya, Foot clearance when crossing obstacles of different heights
with the lead and trail limbs, Gait Posture. 88 (2021) 155–160.
https://doi.org/10.1016/J.GAITPOST.2021.05.020.
[80] S.W. Wu, M.R. Delgado, L.T. Maloney, Economic decision-making comparedwith an equivalent motor task, Proc. Natl. Acad. Sci. U. S. A. 106 (2009) 6088–
6093.
https://doi.org/10.1073/PNAS.0900102106/SUPPL_FILE/0900102106SI.PDF.
[81] D.M. Wolpert, M.S. Landy, Motor control is decision-making, Curr. Opin.
Neurobiol. 22 (2012) 996–1003. https://doi.org/10.1016/J.CONB.2012.05.003.
[82] K. Ota, M. Shinya, L.T. Maloney, K. Kudo, Sub-optimality in motor planning is98

not improved by explicit observation of motor uncertainty, Sci. Rep. 9 (2019) 1–
11. https://doi.org/10.1038/s41598-019-50901-x.
[83] K. Ota, M. Shinya, K. Kudo, Motor planning under temporal uncertainty is
suboptimal when the gain function is asymmetric, Front. Comput. Neurosci. 9(2015) 88. https://doi.org/10.3389/FNCOM.2015.00088.
[84] K. Ota, M. Shinya, K. Kudo, Sub-optimality in motor planning is retained
throughout 9 days practice of 2250 trials, Sci. Rep. 6 (2016) 1–12.
https://doi.org/10.1038/srep37181.
[85] C.M. Said, Mary Galea, Noel Lythgo, Obstacle crossing performance does notdiffer between the first and subsequent attempts in people with stroke, Gait
Posture. 30 (2009) 455–458. https://doi.org/10.1016/J.GAITPOST.2009.07.004.
[86] C.M. Said, P.A. Goldie, A.E. Patla, W.A. Sparrow, Effect of stroke on step
characteristics of obstacle crossing, Arch. Phys. Med. Rehabil. 82 (2001) 1712–
1719. https://doi.org/10.1053/APMR.2001.26247.
[87] Eric R.Kandel, James H. Schwartz, Jessell T.M., Siegelbaum S., Hudspeth A. J.,
Mack S, Keir G.Pearson, James E.Gordon, Principles of Neural Science, in: Fifth
edit, McGraw-Hill, New York, 2000: pp. 821–833.
[88] A.A. Mohagheghi, R. Moraes, A.E. Patla, The effects of distant and on-line
99

visual information on the control of approach phase and step over an obstacle
during locomotion, Exp. Brain Res. 155 (2004) 459–468.
https://doi.org/10.1007/S00221-003-1751-7/TABLES/1.
[89] N.C.W. Chu, D.L. Sturnieks, S.R. Lord, J.C. Menant, Visuospatial working
memory and obstacle crossing in young and older people, Exp. Brain Res.
(2022). https://doi.org/10.1007/S00221-022-06458-9.
[90] H.A. Simon, A behavioral model of rational choice, Q. Jounal Econ. 63 (1955)
99–118. https://academic.oup.com/qje/article/69/1/99/1919737 (accessed
November 12, 2022).
[91] H.A. Simon, Rational choice and the structure of the environment, Psychol. Rev.
63 (1956) 129–138.
[92] R.J. Van Beers, P. Haggard, D.M. Wolpert, The role of execution noise in
movement variability, J. Neurophysiol. 91 (2004) 1050–1063.
https://doi.org/10.1152/JN.00652.2003/ASSET/IMAGES/LARGE/Z9K00204368
70012.JPEG.
[93] J.A. Stevens, E.D. Sogolow, Gender differences for non-fatal unintentional fall
related injuries among older adults, Inj. Prev. 11 (2005) 115–119.
https://doi.org/10.1136/IP.2004.005835.
100

[94] H.Y. Cho, M.J.H. Heijnen, B.A. Craig, S. Rietdyk, Falls in young adults: The
effect of sex, physical activity, and prescription medications, PLoS One. 16(2021) 1–19. https://doi.org/10.1371/journal.pone.0250360.
[95] R. Vitório, E. Lirani-Silva, A.M. Baptista, F.A. Barbieri, P.C.R. Dos Santos, C.
Teixeira-Arroyo, L.T.B. Gobbi, Disease severity affects obstacle crossing inpeople with Parkinson’s disease, Gait Posture. 40 (2014) 266–269.
https://doi.org/10.1016/J.GAITPOST.2014.03.003.
[96] R. Sakurai, K. Kodama, Y. Ozawa, Adaptive locomotion during subtle
environmental changes in younger and older adults, Sci. Rep. 12 (2022) 12438.
https://doi.org/10.1038/S41598-022-16436-4.
[97] N. Chen, X. Xiao, H. Hu, Y. Chen, R. Song, L. Li, Identify the alteration ofbalance control and risk of falling in stroke survivors during obstacle crossing
based on kinematic analysis, Front. Neurol. 10 (2019) 813.
https://doi.org/10.3389/fneur.2019.00813.
[98] L.C. Benson, S.C. Cobb, A.S. Hyngstrom, K.G. Keenan, J. Luo, K.M. O’Connor,
Identifying trippers and non-trippers based on knee kinematics during obstaclefree walking, Hum. Mov. Sci. 62 (2018) 58–66.
https://doi.org/10.1016/J.HUMOV.2018.09.009.
101

[99] K. Takatori, Y. Okada, K. Shomoto, K. Ikuno, K. Nagino, K. Tokuhisa, Effect ofa cognitive task during obstacle crossing in hemiparetic stroke patients,
Physiother. Theory Pract. 28 (2012) 292–298.
https://doi.org/10.3109/09593985.2011.600424.

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Acknowledgments
本研究の遂行にあたり、指導教官として終始多大なご指導を賜った広島大学大学院人間社会科学研究科進矢正宏准教授に深く感謝いたします。同研究科田中亮准教授、並びに中尾敬准教授には本論文作成にあたり、副査として適切なご助言を賜りました。ここに深謝の意を表します。
同じ研究室に所属し、私が挫けるたびに何度も励ましてくれた下田代
祐輔さん、自身も忙しかったにも関わらず図の作成や解析を手伝ってくれた吉本航平さん、私の論文に丁寧なコメントをくれた鹿渡稜太郎さんには深く感謝いたします。本当にありがとうございました。そして本研究に被験者として協力していただいた同大学の学生、研究遂行に必要な経理の手続きをしていただ
いた事務の皆様、並びに私の研究生活を精神的に支えてくれた友人達にも深く感謝いたします。
優れた研究を行うために必要なスキルと知識をご教授くださった東京
都健康長寿医療センター研究所桜井良太先生、並びに同研究所社会参加と地域保健研究チームの皆様にも深く感謝いたします。
最後に、これまでの長い学生生活を物心両面で支え、私が嬉しい時は共に喜び、苦しい時は私に研究を続ける勇気をくれた両親、祖父、叔父達、妹には深く感謝いたします。
103