Jessica Beltran Ullauri*, Yasuhiro Akiyama*, Naomi Yamada†, Shogo Okamoto* and Yoji Yamada* *Dept. of Mechanical Science and Engineering, Nagoya University, Japan Email: jessica.g.beltran@ieee.org, akiyama-yasuhiro@mech.nagoya-u.ac.jp, okamoto-shogo@mech.nagoya-u.ac.jp, yamada-yoji@mech.nagoya-u.ac.jp †Dept. of Physical and Occupational Therapy, Nagoya University, Japan Email: yanagihara.naomi@b.mbox.nagoya-u.ac.jp Abstract —The reduced foot-ground clearance manifested in the healthy elderly is a major cause of tripping, potentially resulting in the loss of balance and falling. Hence, there is a critical need to study the foot-ground clearance deficiencies in the elderly. However, such studies are limited by the risks posed by experimental conditions to the health and safety of this population. As a solution, the present study proposes a new  Muscle  Activity  Restriction  Taping  Technique  (MARTT) to simulate the reduced foot-ground clearance of the elderly in healthy young adults. MARTT aims to restrict the range of contraction of the tibialis anterior and gastrocnemius muscles involved in the ankle's dorsal and plantar flexion, respectively. The effectiveness of MARTT in simulating the reduced foot- ground clearance in continuous walking was verified in three young adults during treadmill and overground walking. The results revealed that MARTT could successfully simulate the reduced clearance, specifically the minimum toe clearance (MTC), and other gait characteristics of the healthy elderly, such as reduced single-support phase, shortened step length, and lower walking speed. Keywords—foot-ground clearance, taping, gait analysis, el- derly, minimum toe clearance
I.  I NTRODUCTION
Falling is considered to be one of the major causes of morbidity and loss of mobility in the elderly [1], [2]. In fact, falling was reported to increase the risk of injury five-fold than any other cause, in the elderly [1]. Furthermore, tripping and stumbling while walking forward has been ranked as the principal cause of falls in this population [3]. In addition, falling can result in the reduction or even elimination of the physical activities of the elderly, including walking, due to the fear of experiencing another fall [1]. Therefore, there is a strong need to prevent falls in the elderly. Several studies have analyzed elderly walking characteristics, documented the development of support machines, and simulated their sensory and motion loss, toward achieving this goal. Studies comparing the gait pattern of the elderly to that of the young have served to determine the main differences contributing to the higher risk of falling. The study of the foot-ground clearance in the young and the elderly has revealed that the elderly exhibit a greater risk of contacting the ground with the swing foot because of the higher variability [4], [5] and lower mean [5], [6] of their minimum toe clearance (MTC). Additionally, owing to the ankle dorsiflexors weakness, the elderly suffer from foot-drop, which leads to a lower clearance to the ground and ends up to be compensated by an excessive hip flexion [7]. Moreover, Winter et al. recorded a reduction in the index of dynamic balance, which indicates a deficiency in balance control in the elderly [8], and therefore, is a potential cause of falling. It has also been revealed that owing to the gait deficiencies, the elderly adapt their gait to a safer pattern that is characterized by an increased double-support phase, decreased push-off power, flat-footed landing and lower walking speed [4], [8]. Effective experimentation in the elderly is restricted to certain experimental conditions that guarantee the safety of the elderly subjects. Further- more, the number of elderly persons willing to participate voluntarily in these experimentations is limited by their fear of experiencing pain or injury. In designing mechanical aids to assist the elderly in walking and reduce the risk of falling, several approaches of ankle foot orthosis (AFO) have focused on providing support to the dorsal flexion in order to prevent foot-drop and increase the foot-ground clearance. For instance, passive AFOs that either utilize embedded pumps under the shoe sole [9], [10] or oil dampers [11] have been developed to prevent foot-drop and foot-slap. In addition, active AFOs that utilize actuators such as series elastic actuators (SEA) [12], and magnetorheological (MR) dampers [13] have been designed to increase foot-ground clearance and prevent foot- drop. As in the survey [14], AFOs have been developed without a further understanding of the most appropriate support of an individual’s gait. Consequently, most AFOs developed to date remain confined to laboratory experiments. Furthermore, the simulation of physiological and cog- nitive impairments of the elderly in the young may be worthwhile in sensitizing medical students and allied health professionals to the full implications of aging, and promote a better understanding of how these disabilities reduce mobility in the elderly. For instance, an Aging Game [15] has been implemented in medical and nursing schools, and care- giving institutions to engage the participants in experiencing chronic physical conditions by utilizing physical props. Sim- ilarly, Wood involved her students in an aging simulation ex- ercise so they could experience the impaired vision, hearing, smell, taste and mobility that afflict the healthy elderly [16]. Even though this field is not fully developed, it can provide insights into the challenges faced by the healthy elderly, and consequently, facilitate the development of suitable solutions to overcome their high risk of falling. The present study proposes a new Muscle Activity Re- striction Taping Technique (MARTT), which restricts the contraction of the gastrocnemius and tibialis anterior mucles, simulating the reduced foot-ground clearance, single-support phase, step length and walking speed that characterize the walking traits of the elderly. MARTT may potentially solve certain aforementioned issues to achieve more effective measures to correct their gait patterns, and prevent falls, by: (i) overcoming the drawback of restricting experimentation to the elderly, and (ii) simulating the former characteristics of the elderly gait in the young.
II.  METHODOLOGY
This study was approved by the institutional review board of Nagoya University, Japan. Of note, several sport-taping techniques conventionally implemented to limit the plantar and dorsal flexion of the ankle were tested before MARTT; however, the obtained results were no satisfactory, which is mainly attributed to the tape loosening effects.
A. Participants
Three male participants, aged 25, 24, and 22 years, weighing 72, 60.2, and 65.2 kg, and 1.74, 1.70 and 1.69 m in height, respectively, were included in this study. All participants were free of any neurological or musculoskeletal impairment. During the study the participants wore comfort- able shoes that allowed a normal dorsal and plantar flexion of the ankle.
B. Muscle Activity Restriction Taping Technique (MARTT)
MARTT was designed to simulate the reduced foot- ground clearance that characterizes the gait of the healthy elderly. MARTT was inspired knowing that the tibialis anterior and gastrocnemius muscles, which are involved in dorsal and plantar flexion of the ankle, respectively [17], can be constrained by restricting the range of contraction of the bundle of muscle fibers. MARTT is performed by placing a tape in the transverse direction of the tibialis anterior and gastrocnemius muscles at the height where the heads of the gastrocnemius end, as depicted in Fig.1. The tape utilized in MARTT is non-stretchable (Nichiban, non-elastic C type tape); therefore, the technique was not affected by its loosening, as commonly observed in sport taping techniques. Consequently, MARTT facilitated a consistent degree of restriction during the experiments. The fidelity of the restriction achieved with MARTT was tested in preliminary experiments that compared the maximum flexion and extension of the participants' ankles before and after walking for more than 3 minutes, and it was verified that the restriction remained stable during continuous walking. MARTT was implemented ensuring that it did not produce pain in the participants while walking.
C. Equipment
A motion capture system (Eagle, Motion Analysis) and a set of markers, located along the body of the participants, as recommended by the motion module of SIMM (Software for Interactive Musculoskeletal Modeling), were used to capture the motion of the lower and upper body of the participants during all the experiments. In addition, four force-plates (M3D FP, Tec Gihan) corresponding to the toe and heel (two for each foot), measured the ground reaction forces while walking. The motion and reaction forces were recorded at 100 Hz. In addition, a treadmill (1.4 × 0.5 m walking surface) and a 7-meter-long even walking lane were used as walking paths, monitored by the motion capture system.
D. Experimental protocol
Fig. 2 shows the protocol followed during each experi- ment. In the subsequent text, normal walking refers to the participant's natural walking patterns with no restriction of motion, and restricted walking refers to walking patterns after MARTT was implemented. First, the marker sets were placed along the participant's body and the force sensors were attached to the shoes. Before the experiment, each participant was instructed to walk for a specified period of time (adaptation time) on the treadmill in order to get accustomed to the shoes and the walking path, and to guarantee natural walking during the experiments. The treadmill speed was set at 4 km/h, which is approximately the normal walking speed of young adults [5]. After the adaptation time, the normal walking of the participant was recorded while walking on the treadmill for 3 minutes and 5 times overground. The order of the recordings was not randomized at this time since it was assumed that minimal exhaustion would occur after treadmill walking. Next, MARTT was implemented, and the participant was instructed to walk on the treadmill for a specified warm- up time, which ensured stable restriction and a uniform walking pattern during the experiment. Following that, the participant walked on the treadmill for 3 minutes and 5 times overground. The order of walking on these two paths was randomized to ensure the results obtained were independent of the experimental order.
E. Data processing
The positions of all markers were computed in Cartesian coordinates, and processed in SIMM to obtain the corre- sponding sagittal-plane motion of the hip, knee and ankle joints. Data from 2 of the 3 minutes of walking on the treadmill were deferred for further processing in order to eliminate the motion as the participant synchronized his walking with the treadmill. The beginning and end of each stride, and the mo- tion corresponding to the swing phase were determined by detecting the heel-contact and toe-off time based on the ground reaction forces. The strides and swing motion were normalized, and then averaged to obtain the participants' characteristic gait cycle i.e. joints' flexion and extension. The toe-to-ground and heel-to-ground clearances, defined as the height from the ground to the markers placed on the metatarsophalangeal joint and calcaneus, respectively, were calculated. The minimum length of both parameters during the entire swing phase was defined as the minimum foot-ground clearance. The MTC, which is observed during 50% to 60% of the swing phase, was computed as the toe clearance at the time when the toe was closest to the ground. Moreover, to analyze MARTT effectiveness further, the angle between the foot and the shin, henceforth refered to as foot-leg angle, was determined during the entire gait cycle. The angle of 0° was considered to represent the foot-leg angle when the participant was standing upright; therefore, a negative angle represents the plantar flexion of the ankle, and a positive one the dorsal flexion of the ankle.
III.
A. Treadmill walking 1) Minimum foot-ground clearance:  All participants had a lower minimum foot-ground clearance during restricted walking than during normal walking. For instance, the minimum foot-ground clearance to the treadmill for the right foot of participant 1 during the swing phase in normal and restricted walking, is illustrated in Fig. 3. Notably,
Mean ± SD (gait phase % in which the MTC ocurred, being 0% the heel-contact of the left foot); *** indicates a significant difference compared with TABLE II: SINGLE-SUPPORT PHASE, DOUBLE-SUPPORT PHASE AND STEP LENGTH IN NORMAL AND RESTRICTED WALKING ON THE TREADMILL
Mean ± SD; *** indicates a significant difference compared with normal walking for p<0.001 and ** for p=0.016
Mean ± SD (gait phase % in which the MTC ocurred, being 0% the heel-contact of the left foot) the motion of the foot maintained the same pattern during restricted walking. Table I shows the MTC for both feet of each participant during normal and restricted walking. The reduction of the MTC during restricted walking was statistically significant (two sample t -test, p<0.001, dof = 340, 318 and 286 for participant 1, 2 and 3, respectively). In addition, the phase percentage in which the MTC ocurred, i.e. instant during swing phase, in both normal and restricted walking was nearly identical for each participant. 2) Joint motion:  During the swing phase, the participants showed a more negative foot-leg angle during restricted walking. The increase was considerable during the middle swing phase. Fig. 4 illustrates the case of participant 1, where the swing phase corresponds to the range of 60% to 100% of the gait cycle. This implies that during the swing phase the ankle underwent higher plantar flexion than normal, explaining the reduced foot-ground clearance during restricted walking, in all participants. These phenomena are similar to those observed in the elderly. Participants 1 and 2 also presented a lower hip flexion, which contributed to the lower foot-ground clearance. Regarding the knee joint motion of each participant, no change in flexion and extension was observed. Moreover, the average hip, knee and ankle motion during restricted walking maintained the same pattern as normal walking in each participant, suggesting that MARTT did not impair the participants' walking patterns. 3) Spatial-temporal parameters: The reduced single- support phase, increased double-support phase and shorter step length that characterize the elderly gait were signifi- cantly simulated in participant 1 and 2, as shown in Table II. Participant 3 differed from the others in that his single- and double-support phases remained practically unchanged, and his step length increased during restricted walking. A thorough analysis clarified that participant 3 showed longer step length because one of the intrinsic characteristics of his normal gait on the treadmill was maintained even after MARTT was implemented. His natural walking pattern on the treadmill was characterized by a longer single-support
Mean土SD phase, as seen in Table II, suggesting that he spent more time. on the swing phase and moved the hip further to the front, thus reaching longer distances than the other participants. This behaviour was also verified when analyzing the time each participant took from the instant of heel-contact to the instant when the hip started to extend, as the body was moving forward. Participant 1 and participant 2 took around 10% of their gait cycle to accomplish this, however, participant 3 took around 4%, implying that participant 3 moved the hip further as his heel contacted the walking path, leading to higher extension of the hip and longer step length. These phenomena explain the longer step length of participant 3 even though his clearance was reduced during restricted walking; this pattern occurred only during treadmill walking. Several studies have proved that people are likely to alter their normal gait (overground) when walking on a treadmill, specifically in terms of greater hip extension [18], which was the case for participant 3. During restricted walking, participants 1 and 2 presented a higher cadence on the treadmill as their step lengths were reduced, and in order to match the treadmill's speed, they had to take more steps than normal. In contrast, participant 3 presented a lower cadence owing to his longer step length.
B.  Ground walking
As the data obtained during the overground walking setup were limited to 4 steps for each of the 5 experiments conducted per subject, the corresponding results are not said to be statistically significant; however, they indicate the effectiveness of MARTT. 1) Minimum foot-ground clearance:  All participants pre- sented a lower foot-ground minimum clearance during swing phase, as illustrated in the case of participant 1 in Fig. 5. Of note, MARTT did not alter the foot motion pattern. Furthermore, Table III shows that MARTT also reduced the participants' MTC when walking overground, and there were no significant differences between normal and re- stricted walking in the percentage of the gait cycle during which MTC occured. 2) Joint motion:  The right foot-leg angle of participant 1 is illustrated in Fig. 6. In agreement with the treadmill walking, all participants presented a higher negative foot-leg angle during the middle swing phase i.e. the plantar flexion of the foot was larger; which explains the reduction of the MTC during the restricted walking. 3) Spatial-temporal parameters: Table IV suggests the effectiveness of MARTT in reducing the single-support phase, step length and walking speed, and in increasing the double-support phase for all the participants during overground walking. Owing to the reduced step length and walking speed, all participants exhibited lower cadence during restricted walking. Of note, the step length of participant 3 was reduced during overground walking, indicating that the failure in sim- ulating in this participant the aforementioned characteristics during treadmill walking is attributed to the treadmill.
IV. D ISCUSSION
MARTT can be a valuable tool for further analyzing the walking performance in the healthy elderly, specifically when the elderly cannot participate in studies where the experimental conditions may jeopardize their safety, such as falling-risk analysis and studies on their ability to avoid obstacles. For instance, MARTT can be utilized to analize the risk of tripping due to foot-ground clearances that are lower than normal. However, as MARTT restricts absolute motion, the neurological and biomechanical responses of the elderly are not accounted for; therefore, this technique may be restricted to studies where the results would not depend on these responses. Moreover, as MARTT can specifically simulate the gait characteristics of the elderly without altering the motion of the hips, knees, and ankles, it may facilitate experimental studies by eliminating the bias from undetected pathologies in the elderly. However, MARTT cannot simulate accurately a certain range of restriction due to the uncontrollability of the strength of the taping. The implementation of a mech- anism to adjust the fastening and fixing strength, replacing the function of the tape, may constitute a solution to this issue. Statistical analysis is further necessary to determine the limit period during which MARTT is effective in subject's continuous walking.
CONCLUSION
V.
In this study, MARTT (Muscle Activity Restriction Taping Technique) was developed with the objective of providing a means to study the elderly gait without facing experimental restrictions that are usually imposed to guaran- tee the safety of this population. MARTT aims to simulate the reduced foot-ground clearance, commonly affecting the healthy elderly walking, in young adults. In order to verify the effectiveness of the technique, MARTT was tested in two different experimental setups including treadmill and overground walking. The results revealed that MARTT suc- cessfully simulated the aforementioned characteristic and the reduction of the single-support phase, step length and walking speed, which also characterize the natural walking patterns of the healthy elderly. This research was supported by JSPS KAKENHI, grant number 26750121. The authors are indebted to Prof. Hi- rokazu Kobayashi for valiant discussion about taping tech- niques.