Bulletin of the JSME

Vol.14, No.1, 2019

Journal of Biomechanical Science and Engineering
Experimental analysis of the fall mitigation motion caused bytripping based on the motion observation until shortly before
ground contact
Yasuhiro AKIYAMA∗ , Kento MITSUOKA∗ , Shogo OKAMOTO∗ and Yoji YAMADA∗∗ Depertment of Mechanical Systems Engineering, Nagoya University

Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8603, Japan
E-mail: yasuhiro.akiyama@mae.nagoya-u.ac.jp

Received: 26 November 2018; Revised: 7 March 2019; Accepted: 11 April 2019

Abstract
This study focuses on observing and analyzing the occurrence of a fall for humans during normal gait, whichperhaps results in severe injury. Previously, the insuﬃciency of a recovery step, which diminishes the forward
rotation of the body after tripping, was suggested as a factor for the failure of fall avoidance motion. However,
although it was identified that a slow and/or short recovery step resulted in the failure of fall prevention, the physicalprocess of tripping and falling during the gait was not analyzed suﬃciently. In this study, the subject’s reaction
motion and fall process against tripping became clearer because the fall motion, which included the phase closer
to the ground contact, could be recorded for a longer time than that in most previous studies. Although the subject
attempted to mitigate the forward angular momentum and the descent of body induced by tripping by holding on
his recovery foot, it was not eﬀective, especially when the recovery step length was short. Among such trials,
the larger forward inclination of the body, the excessive forward movement of the center of mass from the support
point, and the smaller ground reaction force of the recovery foot in the normal direction was observed. Because theshort recovery step resulted in the limitation of the moment arm, which aﬀected the reaction torque of the recovery
foot, it became diﬃcult to decelerate the body rotation and prevent the fall. Furthermore, it was also suggested thatthe forward lean of the body and the decrease of the ground reaction force increased the impact speed and eﬀective
mass, which aﬀected the impact force. The observation of such an advanced fall phase also contributes to a more
realistic simulation of the human reaction motion for a more precise estimation of the fall injuries.
Keywords : Trip and fall, Reaction motion, Severity estimation, Fall experiment, Unavoidable fall

1. Introduction
Injuries caused by fall are one of the major risks for the elderly. A recent study indicates that approximately 10 to
30% of the elderly have experienced a fall (Niino et al., 2000). Furthermore, approximately 10% of those who fell wereseriously injured and had limitations in their daily activity (Luukinen et al., 2000). Even after they were physically cured,
the fear of the fall probably prolonged their inactivity, which resulted in a decrease of their quality of life (Arfken et al.,1994). Moreover, falls are a major cause of injuries for workers in factories or construction sites (Tate, 1992; Lipscomb
et al., 2006).
Unfortunately, although the fall mechanism is studied to prevent and mitigate injuries, there are limited opportunities
to observe a natural fall with suﬃcient measurement parameters (Robinovitch et al., 2013). Thus, the knowledge obtainedin fall experiments is useful to understand fall motion quantitatively. The results of previous fall experiments suggest
the existence of two fall avoidance strategies against tripping: elevating and lowering (Eng et al., 1994). Tripped people
sometimes overcome an obstacle by elevating a tripped leg too soon without moving the position of the stance foot. Then,the elevated leg is stepped forward. Otherwise, people step the tripped leg on-site instantaneously and subsequently step
the other leg forward. The former is the elevating and the latter is the lowering strategy. As mentioned above, a long
Paper No.18-00510
J-STAGE Advance Publication date : 18 April, 2019
[DOI: 10.1299/jbse.18-00510]© 2019 The Japan Society of Mechanical Engineers

1

Akiyama, Mitsuoka, Okamoto and Yamada, Journal of Biomechanical Science and Engineering, Vol.14, No.1 (2019)

forward step, which is called the recovery step, commonly appears among these strategies. According to the observationof the reaction motion of the elderly after tripping by Pavol et al., a quicker and longer recovery step was essential to stop
the forward rotation and descent of the body to avoid a fall (Pavol et al., 2001). Other groups have also suggested theimportance of the recovery step (Grabiner et al., 1993; Smeesters et al., 2001a).
However, the fall motion during a critical or terminal phase cannot be obtained in an experiment because it is unsafe
for the subject, which means that it has to be intercepted before contacting the ground (Pavol et al., 2001; Owings et al.,2001) or performed in a designated area (Smeesters et al., 2001b). Otherwise, the fall avoidance motion must be used,which does not require an actual fall (Pijnappels et al., 2005; Eng et al., 1994). Meanwhile, although motion simulation
is used to analyze the fall motion (DeGoede et al., 2003a; Lo et al., 2008), implementing fall avoidance and humanmitigation motion into this simulation is diﬃcult because of the imperfect study of such motions. One reason for the
diﬃculty of simulating the fall motion is that the fall motion recorded in the experiment is too short, which means thesimulation should start from the early phase of the fall (Zhou et al., 2002). Although a longer duration of motion should
be simulated to estimate the reaction motion of humans, it is diﬃcult to anticipate it.
Thus, the observation and analysis of the successive motion after the failed fall avoidance motion, which is the motion
when the recovery step cannot stop the fall, is essential to understand the mechanism of the fall process and injuries causedby the ground contact. The present study conducted a series of fall experiments to observe the reaction motion against
tripping, which resulted in the fall, to further understand the fall motion.

2. Methods
The experiment was performed with the permission of the institutional review board of Nagoya University.
2.1. Subject
Subjects were recruited from the student population of Nagoya University. Screening of the applicants revealed no
gait disorders. Thus, all the applicants participated in the experiment. Seven healthy male young adults with a mean ageof 21.4 years old and standard deviation (SD) of 1.2 participated in the experiment. Their mean height and weight were
172.9 cm (±3.2 SD) and 61.0 kgf (±7.6 SD), respectively. Their average body mass index was 20.4 and ranged from 16.7
to 23.6.
2.2. Apparatus
Each experiment was conducted in an approximate 5 × 8 m area, in which motion was recorded at 100 Hz using athree-dimensional motion capture system (MAC 3D System, Motion Analysis Corporation, US). A total of 37 markers,
including cluster markers, were attached, as shown in Fig. 1. Subsequently, a pole was hung in front of the subject andmoved at a constant speed, in between 1.3 to 1.4 m/s, using an electric motor to stabilize the subject’s gait speed andprevent the subject from reducing the gait speed after the tripped trial, which was observed in the preliminary experiment.
In addition, a metronome was used to maintain a constant gait rhythm. The rhythm of the metronome was tuned for eachsubject to be able to walk naturally.
The ground reaction force (GRF) was recorded at 100 Hz using four mobile six-axis force plates (M3D, Tech Gihan
Co., Ltd., Japan) fixed under the toe and the heel of both feet. A bar was fixed in the lane from the side at a height of
25 cm to trip the subject. Some previous studies used a flat plate with a height of approximately 10 mm (Eng et al., 1994;
Pijnappels et al., 2001; Wang et al., 2012). However, a bar, which also causes falls in the daily living environment, wasselected to increase the probability of a fall in this study. The contact force on the bar was measured using two three-axis
force sensors (USL08-H6-2KN-C, Tech Gihan Co., Ltd., Japan). The subjects wore goggles with the lower half covered,to hide the bar from sight and prevent the anticipation of tripping. Moreover, each subject’s ankle was connected to a static
object using a rope to control the length of the recovery step after tripping. Its tension force was measured by a load cell
(RSCC-200 kg, Unipulse Corporation, Japan). Because the subject employed the “lowering” strategy in all preliminary
trials, the rope was connected to the recovery leg, which was the opposite leg to the tripped side. The safety harness washung using an air spring from the gondola, which moved along the lane with the pole using an electric motor. The safety
harness did not interfere with the gait motion of the subject because it slacked in the standing posture. Another load cell
fixed to the harness was used to measure the supporting force. Figure 2 shows the experimental setup.

[DOI: 10.1299/jbse.18-00510]© 2019 The Japan Society of Mechanical Engineers

2

Akiyama, Mitsuoka, Okamoto and Yamada, Journal of Biomechanical Science and Engineering, Vol.14, No.1 (2019)&ƌŽŶƚŚĞĂĚ,ĞĂĚZĞĂƌŚĞĂĚ

^ŚŽƵůĚĞƌ
ůĂǀŝĐůĞ

W^/^
ůďŽǁ

tƌŝƐƚ

'ƌĞĂƚĞƌƚƌŽĐŚĂŶƚĞƌ
>ĂƚĞƌĂů
ƚŚŝŐŚ

<ŶĞĞ
&ŝďƵůĂƌŚĞĂĚ,ĞĞů
Fig. 1

^/^

ŶŬůĞ

hƉƉĞƌ
ƚŚŝŐŚ&ƌŽŶƚƐŚĂŶŬ
dŽĞ

Marker set Markers were attached to the top, rear, and front of the subject’s head, shoulders, clavicle,
elbows, wrists, anterior and posterior superior iliac spines (ASIS and PSIS), front and lateral thighs, knees,
fibular heads, shanks, ankles, heels, and toes. Markers were attached on each feature point or at the rotation
center of each joint. Markers on the right and left sides were attached symmetrically. Cluster markers,
which was the rigid branch with three markers and estimated the position of the root using these markers,
were used for superior iliac spines. A total of 37 markers were used.

2.3. Protocol
The experiment process was explained to each subject and each signed a consent form. Subjects wore well-fitted
sportswear with reflective markers and shoes, in which force plates were installed. Safety gear and ropes were also
attached. Then, the subject started to walk in the walking lane repeatedly.
The subjects were instructed to walk in a straight line to the hanging target placed at the extension of the walking
lane. Before starting to walk, the subjects walked in place for five steps to adjust their gait timing to the metronome ineach trial. Dummy trials, which did not include tripping, were randomly performed during tripping trials to prevent the
subject’s anticipation. The combinations of tripping conditions, which denoted the length of the limitation of the recovery
step and the side of the tripped leg, were randomized. Thus, the position of obstacle and rope connection was switched
for each condition between trials. In the tripped trials, two diﬀerent restrictions regarding the recovery step, which had
diﬀerent limitations in terms of the step length, named short-step and long-step were used. A total of 35 trials included
23 non-tripped control cases, six short-step lengths, six long-step lengths were recorded for each subject. The number oftripped trials was the same for the right and left sides.
In this study, the position of the obstacle was adjusted to trip the subject in the middle to late swing phase, when therisk of injury becomes higher, as discussed previously (Mitsuoka et al., 2015; Dietz et al., 1986). However, the young
adults seldom fell when tripped because they could perform suﬃcient recovery motion. According to a study on the failed
recovery motion after tripping, the recovery step of fallers was shorter and slower than that of non-fallers (Pavol et al.,2001). Thus, in this study, a failed recovery step was artificially caused by limiting the step length of the recovery stepusing a rope, which connected the ankle of the subject to an object fixed at the rear part of the walking lane, to observe thefall motion constantly. The rope length was adjusted so that the recovery leg did not exceed the bar position in forward
direction in the short-step case. The rope length was adjusted so that the recovery leg did not exceed the bar position
in forward direction in the short-step case. In contrast, the rope length in the long-step case was extended by 20 cm.
Thus, the recovery step could become longer to resist forward falls more eﬀectively. The rope length of each condition
was adjusted beforehand to be the same as the position of the obstacle. The restriction force was monitored to identify
whether the tripping condition was stable.
2.4. Data Processing
The recorded data were smoothed using a 6 Hz Butterworth filter. The trials, in which the marker was criticallyhidden, were not used in the analysis. The joint angles were calculated by fitting the motion of the markers to the humanmodel of SIMM (Mulsculographics Inc., U.S.) using the least-squares method. The position of the center of mass (CoM)of the whole body was calculated using Zatsiorsky’s method (De Leva, 1996). The trunk angle was determined as theangle of the line, which connected the center of the shoulder markers and the center of the hip markers, from the vertical[DOI: 10.1299/jbse.18-00510]© 2019 The Japan Society of Mechanical Engineers

23

Akiyama, Mitsuoka, Okamoto and Yamada, Journal of Biomechanical Science and Engineering, Vol.14, No.1 (2019)

0RWLRQFDSWXUHFDPHUDV
0HWURQRPH

ᅅ/RDGFHOOV$FWXDWHGOLQHDUVOLGHU

6SHHG JXLGH
6DIHW\KDUQHVV

0RWRU

7ULSSLQJ SODWH

5RSH)RRWIRUFHSODWHV

2EVWDFOH

D[LVIRUFHVHQVRUV

6SHHGJXLGHLVGULYHQE\0RWRU
6XEMHFWZDONVDORQJZLWK6SHHGJXLGHDWUK\WKPRI0HWURQRPH

Fig. 2

Experimental setup A bar, which trips the subject, was fixed in the lane from either side. The subject’s
ankle was connected to a static object using a rope to control the length of the recovery step. The subject
was supported by the safety harness when he fell.

direction (Wang et al., 2012). The GRF of each leg was calculated as the sum of both the toe and heel plates. The
position of the center of pressure (CoP) was calculated as the weighted center of GRF of each force plate. The positionof each force plate in global coordinates was obtained from the motion capture. Then, CoM-CoP distance, which was therelative position of CoM from CoP in the traveling direction, was determined as the parameter of body balance and fall
severity. The timing of the heel contacts and the toe oﬀs was determined based on the normal direction of GRF with a
10 N threshold. The duration between successive heel contacts of the same leg was determined as the gait cycle (GC).
Fall trials were extracted from tripped trials and analyzed in this study. The trial, in which 50% of the body mass
was supported by the harness, was determined as the fall trial. This threshold value was designed so that the subject
could not avoid falling when the supporting force exceeded it. Furthermore, to avoid the eﬀect of the harness tension on
reaction motion, the motion before the force extracted at the harness exceeded 50 N were analyzed. The tripping timing
was detected when the force exerted at the bar increased by 20 N.
All trials herein were classified as the “lowering strategy,” wherein the tripped leg was lowered and the other leg
stepped forward too soon. This preference matched the previously reported relationship between the tripping phase andthe fall avoidance strategy (Eng et al., 1994; Schillings et al., 2000). Four motion events were defined during the fallmotion. The tripped timing (TRT) was defined as the timing of tripping. The subject lowered the tripped leg and touched
the floor at the timing of the lowering step contact (LSC). The recovery step contact (RSC) was defined as the timing when
the recovery leg touched the floor. Meanwhile, the timing when the support force of the harness exceeded the thresholdowing to a subjects fall was defined as fall detected timing (FDT).
The GRF, step length, and CoM position were normalized based on the mass and height of each subject. The
peak GRF was extracted from the lowering step and recovery step to evaluate the performance of fall mitigation. Whenevaluating the mean values of the gait parameters, we considered all trials uniformly. The diﬀerence of the motion
parameter between the conditions was tested using the Mann-Whitney U-test.

3. Results
A total of 58 fall trials, which consisted of 29 short- and 29 long-step length cases, were analyzed. A typical fallmotion is displayed in Fig. 3. All tripped trials were determined as the fall trial because the subject was finally fully
supported by the safety harness. The trials with unintended trip timing, marker hiding, and other irregular motions were
not processed. The average trip timing was 32.0 ± 3.7% GC.
The gait parameters of normal walking trials were computed from all the subjects to validate the normal gait motion.
The means and the SDs of the gait parameters were calculated as follows: walking speed, 1.34 ± 0.07 m/s; cadence,
110.6 ± 3.8 step/min; step length, 73.1 ± 6.6 cm; and double support ratio, 20.0 ± 2.6%. Compared to a typical normal
gait (Öberg et al., 1993), the subjects in the present experiment walked slightly slow with longer strides.
The tripping timing, peak impact force, and peak restricting force between the two recovery step length conditions[DOI: 10.1299/jbse.18-00510]© 2019 The Japan Society of Mechanical Engineers

24

Akiyama, Mitsuoka, Okamoto and Yamada, Journal of Biomechanical Science and Engineering, Vol.14, No.1 (2019)

Fig. 3

TRT

LSC

RSC

FDT

Images of a typical falling motion observed in the experiment The posture of each timing, tripped timing,
lowering step contact, recovery step contact, and fall detected timing is displayed. The right ankle of thesubject tripped over the bar at TRT in this trial. Then, he lowered the tripped foot and it touched to theground at LSC. Although the subject then moved his left leg forward, it was disturbed by the rope fixed
to the left ankle. Thus, the step length of the recovery step was shortened at RSC. Finally, the subject was
supported by the safety harness at FDT

did not significantly diﬀer (p > 0.1). The recovery step lengths were 11.8 ± 6.1%bh and 28.7 ± 5.8%bh in the short- andlong-step cases, respectively. In contrast, the timing of the recovery step after tripping did not significantly diﬀer between
the short (0.53 ± 0.08 s) and long (0.54 ± 0.05 s) steps.
The fall motions between the short- and long-step cases were compared in terms of the timing of the TRT, LSC,
RSC, and FDT. Figures 4 to 6 show the boxplot of the representative fall motion parameters. Figure 7 summarizes therepresentative motion of the two conditions.
The fall progress is represented by the CoM height, trunk angle, and their velocities (Fig. 4 and Fig. 5(a) and (b)).
A rapid decrease in the CoM height and a large CoM velocity at the timing of RSC and FDT expressed the descent ofbody as the fall progression. Furthermore, the CoM velocity in the traveling direction became lower at the RSC and FDT(Fig. 5(c)). The change of CoM velocity in the horizontal and vertical directions suggested that the gait speed transformed
into a descent velocity when the fall progressed. At the same time, the increase in the trunk angle indicated the forwardtilt, as shown in Fig. 7.
The CoM-CoP distance indicated the forward movement of the body from the support point, which occurred in theunbalanced posture before fall (Fig. 5(d)). When the CoM-CoP distance increased, the CoM lies excessively ahead of the
support point because the supporting area could not expand owing to the insuﬃcient recovery step, whereas the inertia
moved the body forward. The peak normal GRF stood for the reaction force to stop the body descent that occurred during
the fall progression (Fig. 6).

4. Discussion
The decrease of CoM height, increase of trunk angle, and transformation of CoM speed from horizontal direction tovertical direction were commonly observed among fall trials. Because these trends were those of the fall motion, whichmeant the subject could not compensate for the forward angular momentum imposed by tripping (Pijnappels et al., 2005),
they commonly appeared regardless of the subject and rope length.
However, the diﬀerence of the recovery step length aﬀected the rotation and descending speed of the fall as the fallprogressed. Although the CoM height at the FDT did not significantly diﬀer because the force threshold of fall detection
was common, the diﬀerence of the CoM vertical velocity, which aﬀected the fall injuries (DeGoede et al., 2002), became
significantly higher in the short-step case (Fig. 5(b)). Instead, the CoM velocity in the traveling direction became lower
at the RSC and FDT in the short-step case. These diﬀerence of CoM velocities suggested that the major direction of
the motion of CoM diﬀered between the short and long recovery steps because their magnitudes were almost the same.
[DOI: 10.1299/jbse.18-00510]© 2019 The Japan Society of Mechanical Engineers

25

Akiyama, Mitsuoka, Okamoto and Yamada, Journal of Biomechanical Science and Engineering, Vol.14, No.1 (2019)(a) Forward inclination angle of trunk

Fig. 4(b) Angle velocity of trunk inclination

Body inclination and its velocity at the timing of fall events Box represents the first and third quartiles.
Outliers, which are separated from the quartile more than 1.5 times the interquartile range, are marked asa cross. *:p < 0.1, **:p < 0.01(a) CoM height(c) CoM velocity in traveling direction(b) CoM velocity in vertical direction(d) Distance of CoM from CoP
in traveling direction

Fig. 5

CoM position and motion at the timing of fall events Box represents the first and third quartiles. Outliers,
which are separated from the quartile more than 1.5 times the interquartile range, are marked as a cross.
*:p < 0.1, **:p < 0.01

Furthermore, higher trunk inclination at FDT in the short-step case (Fig. 4) suggested that the forward angular momentum
caused by tripping was not mitigated as eﬀectively in the short-step case compared to the long-step case (Pavol et al.,2001).
The performance of mitigation motion could be considered from the CoM-CoP distance and the peak GRF. To
decrease the impact force of ground contact, it was required to reduce the fall speed, which was represented by the verticalvelocity of CoM. Thus, the large peak normal GRF, which helped to decelerate the descent of CoM, became essential.
However, the large CoM-CoP distance made it diﬃcult to exert GRF because of the loss of balance. Furthermore, when
the CoM-CoP distance is large, the large GRF in the normal direction generates a moment toward forward rotation, which
is another factor of a fall (Pavol et al., 2001; Pijnappels et al., 2005). Thus, pushing the ground to mitigate the descending[DOI: 10.1299/jbse.18-00510]© 2019 The Japan Society of Mechanical Engineers

26

Akiyama, Mitsuoka, Okamoto and Yamada, Journal of Biomechanical Science and Engineering, Vol.14, No.1 (2019)

Fig. 6

Peak normal GRF at the timing of fall events Box represents the first and third quartiles. Outliers, which
are separated from the quartile more than 1.5 times the interquartile range, are marked as a cross. *:p < 0.1,**:p < 0.01

Fig. 7

Typical falling motion trajectory with diﬀerent recovery step length Thick line shows recovery leg, thinline shows lowering leg

body speed became diﬃcult in the short-step case at the RSC (Fig. 6). This result revealed that the CoM-CoP distanceaﬀected not only the balancing performance of the upstanding posture and normal gait (Hof et al., 2005; Hof, 2007;
Winter, 1995), but also the mitigation motion against fall.
The ground impact force associated with a fall is an essential factor that determines the severity of injuries. However,
it is impossible to actually measure such force because of ethical reasons. Thus, a model, which estimated the impact
force from eﬀective mass and speed at impact with the floor, was developed (DeGoede et al., 2003b). The eﬀective mass,
which aﬀects the load applied to the impact area, is sometimes estimated as a part of body mass, especially when the
body is supported by multiple contact points. Even in this study, the recovery leg supported most of body mass. However,the contribution of recovery leg probably decreased as CoM separated from the leg. Thus, the increase of CoM-CoP
distance corresponded to the increase of the eﬀective mass. In contrast, the vertical velocity of CoM and angular velocityof the trunk represents the fall speed. Although the large degree of freedom of body motion at the terminal phase of fall
made it diﬃcult to estimate the part and speed of impact, increase of these parameters suggested the increase of injury
risk. Thus, our result suggested that the short-step case, whose CoM-CoP distance and CoM descending speed increased,
would probably result in severe contact, in addition to less likelihood of avoiding a fall. Our result would also help in
estimating the eﬀective mass by extrapolating the observed fall motion.

5. Conclusion
A fall experiment, in which the subject would experience an actual fall, if not for a safety harness, was conducted[DOI: 10.1299/jbse.18-00510]© 2019 The Japan Society of Mechanical Engineers

27

Akiyama, Mitsuoka, Okamoto and Yamada, Journal of Biomechanical Science and Engineering, Vol.14, No.1 (2019)

to further understand the function of a recovery step against tripping during gait. Hence, the actual fall motion in theadvanced phase, which was closer to the critical phase, was recorded and analyzed. The comparison of the physicalparameters between diﬀerent recovery step lengths identified the eﬀect of it on the fall progression. Although the motion
caused by the forward angular momentum caused by tripping was commonly observed, forward rotation and body descentcould not be mitigated, especially in the short-step case. Furthermore, excessive forward sway of the CoM from the
supporting point in the short-step case made it diﬃcult to support the body because of the decrease of the GRF in thenormal direction. This finding is important in estimating fall injuries or developing a mitigating method.

Acknowledgments
We thank the support by JSPS KAKENHI Grant Number 26750121 and the support of our group members, Ikuma
Higo, Ryota Kushida, and Beltran Jessica. This work was supported by METI “Strategic international standardization
promotion project: International standardization of human tolerance against fall injuries”.

References
Arfken, C. L., Lach, H. W., Birge, S. J., and Miller, J. P., The prevalence and correlates of fear of falling in elderly persons
living in the community, American Journal of Public Health, Vol.84, No.4 (1994), pp. 565-570.
De Leva P., Adjustments to Zatsiorsky-Seluyanov’s segment inertia parameters, Journal of Biomechanics, Vol.29, No.9
(1996), pp. 1223-1230.
DeGoede, K. M., and Ashton-Miller, J., Fall arrest strategy aﬀects peak hand impact force in a forward fall, Journal of
Biomechanics, Vol.35, No.6 (2002), pp. 843-848.
DeGoede, K. M., and Ashton-Miller, J., Biomechanical simulations of forward fall arrests: eﬀects of upper extremityarrest strategy, gender and aging-related declines in muscle strength, Journal of Biomechanics, Vol.36, No.3 (2003),
pp. 413-420.
DeGoede, K. M., Ashton-Miller, J., and Schultz, A., Fall-related upper body injuries in the older adult: a review of thebiomechanical issues, Journal of Biomechanics, Vol.36, No.7 (2003), pp. 1043-1053.
Dietz ,V., Quintern, J., Boos, G., and Berger, W., Obstruction of the swing phase during gait: phase-dependent bilateralleg muscle coordination, Brain Research, Vol.384, No.1 (1986), pp. 166-169.
Eng, J. J., Winter, D. A., and Patla, A. E., Strategies for recovery from a trip in early and late swing during human walking,Experimental Brain Research, Vol.102, No.2 (1994), pp. 339-349.
Grabiner, M. D., Koh, T. J., Lundin, T. M., and Jahnigen, D. W., Kinematics of recovery from a stumble, Journal ofGerontology, Vol.48, No.3 (1993), pp. M97-M102.
Hof, A., Gazendam, M., and Sinke, W., The condition for dynamic stability, Journal of Biomechanics, Vol.38, No.1
(2005), pp. 1-8.
Hof, A. L., The equations of motion for a standing human reveal three mechanisms for balance, Journal of Biomechanics,
Vol.40, No.2 (2007), pp. 451-457.
Lipscomb, H. J., Glazner, J. E., Bondy, J., Guarini, K., and Lezotte, D., Injuries from slips and trips in construction,
Applied Ergonomics, Vol.37, No.3 (2006), pp. 267-274.
Lo, J., and Ashton-Miller, J., Eﬀect of pre-impact movement strategies on the impact forces resulting from a lateral fall,
Journal of Biomechanics, Vol.41, No.9 (2008), pp. 1969-1977.
Luukinen, H., Herala, M., Koski, K., Honkanen, R., Laippala, P., and Kivelä, S. L., Fracture risk associated with a fallaccording to type of fall among the elderly, Osteoporosis International, Vol.11, No.7 (2000), pp. 631-634.
Mitsuoka, K., Akiyama, Y., Yamada, Y., and Okamoto, S., Analysis of Skip Motion as a Recovery Strategy after an
Induced Trip, In: 2015 IEEE International Conference on Systems, Man, and Cybernetics, (2015). pp. 911-916.
Niino, N., Tsuzuku, S., Ando, F., and Shimokata, H., Frequencies and circumstances of falls in the National Institute forLongevity Sciences, Longitudinal Study of Aging (NILS-LSA), Journal of Epidemiology, Vol.10, No.1sup (2000) pp.
90-94.
Öberg, T., Karsznia, A., and Öberg, K., Basic gait parameters: reference data for normal subjects, 10-79 years of age,
Journal of Rehabilitation Research and Development, Vol.30 (1993), pp. 210-210.
Owings, T. M., Pavol, M. J., and Grabiner, M. D., Mechanisms of failed recovery following postural perturbations on a

[DOI: 10.1299/jbse.18-00510]© 2019 The Japan Society of Mechanical Engineers

28

Akiyama, Mitsuoka, Okamoto and Yamada, Journal of Biomechanical Science and Engineering, Vol.14, No.1 (2019)

motorized treadmill mimic those associated with an actual forward trip, Clinical Biomechanics, Vol.16, No.9 (2001),
pp. 813-819.
Pavol, M. J., Owings, T. M., Foley, K. T., and Grabiner, M. D., Mechanisms leading to a fall from an induced trip in
healthy older adults, The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol.56, No.7
(2001), pp. M428-M437.
Pijnappels, M., Bobbert, M. F., and van Dieën, J. H., Changes in walking pattern caused by the possibility of a tripping
reaction, Gait & Posture, Vol.14, No.1 (2001), pp.11-18.
Pijnappels, M., Bobbert, M. F., and van Dieën, J. H., Push-oﬀ reactions in recovery after tripping discriminate young
subjects, older non-fallers and older fallers, Gait & Posture, Vol.21, No.4 (2005), pp. 388-394.
Robinovitch, S. N., Feldman, F., Yang, Y., Schonnop, R., Leung, P. M., Sarraf, T., et al., Video capture of the circumstancesof falls in elderly people residing in long-term care: an observational study, The Lancet, Vol. 381 (2013), pp. 47-54.
Schillings, A., Van Wezel, B., Mulder, T., and Duysens, J., Muscular responses and movement strategies during stumblingover obstacles, Journal of Neurophysiology, Vol.83, No.4, (2000), pp. 2093-2102.
Smeesters, C., Hayes, W. C., and McMahon, T. A., The threshold trip duration for which recovery is no longer possible isassociated with strength and reaction time, Journal of Biomechanics, Vol.34, No.5 (2001), pp. 589-595.
Smeesters, C., Hayes, W. C., and McMahon, T. A., Disturbance type and gait speed aﬀect fall direction and impact
location, Journal of Biomechanics, Vol.34, No.3 (2001), pp. 309-317.
Tate, D. G., Workers’ disability and return to work, American Journal of Physical Medicine & Rehabilitation, Vol.71,
No.2 (1992), pp. 92-96.
Wang, T. Y., Bhatt, T., Yang, F., and Pai, Y. C., Adaptive control reduces trip-induced forward gait instability among
young adults, Journal of Biomechanics, Vol.45, No.7 (2012), pp. 1169-1175.
Winter, D. A., Human balance and posture control during standing and walking, Gait & Posture, Vol.3, No.4 (1995), pp.
193-214.
Zhou, X., Draganich, L. F., and Amirouche, F., A dynamic model for simulating a trip and fall during gait, Medical
Engineering & Physics, Vol.24, No.2 (2002), pp.121-127.

[DOI: 10.1299/jbse.18-00510]© 2019 The Japan Society of Mechanical Engineers

29