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Effect of Common Pavements on Interjoint Coordination of Walking with and without Robotic Exoskeleton

Effect of Common Pavements on Interjoint Coordination of Walking with and without Robotic... Hindawi Applied Bionics and Biomechanics Volume 2019, Article ID 5823908, 8 pages https://doi.org/10.1155/2019/5823908 Research Article Effect of Common Pavements on Interjoint Coordination of Walking with and without Robotic Exoskeleton 1 2 2 2 1 Jinlei Wang, Jing Qiu , Lei Hou, Xiaojuan Zheng, and Suihuai Yu Northwestern Polytechnical University, China University of Electronic Science and Technology of China, China Correspondence should be addressed to Jing Qiu; qiujing@uestc.edu.cn Received 22 March 2019; Revised 23 July 2019; Accepted 2 September 2019; Published 1 October 2019 Guest Editor: Michelle Johnson Copyright © 2019 Jinlei Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. The analysis and comprehension of the coordination control of a human gait on common grounds benefit the development of robotic exoskeleton for motor recovery. Objective. This study investigated whether the common grounds effect the interjoint coordination of healthy participants with/without exoskeletons in walking. Methods. The knee-ankle coordination and hip-knee coordination of 8 healthy participants in a sagittal plane were measured on five kinds of pavements (tiled, carpet, wooden, concrete, and pebbled) with/without exoskeletons, using the continuous relative phase (CRP). The root mean square of CRP (CRP ) over each phase of the gait cycle is used to analyze the magnitude of dephasing between joints, and the standard RMS deviation of CRP (CRP ) in the full gait cycle is used to assess the variability of coordination patterns between joints. SD Results. The CRP of the carpet pavement with exoskeleton is different from that of other pavements (except the Hip-Knee/RMS tiled pavement) in the midstance phase. The CRP on the pebble pavement without exoskeleton is less than that Hip-Knee/RMS on the other pavements in all phases. The CRP of the pebble pavement without exoskeleton is smaller than that Hip-Knee/SD of other pavements. The CRP with/without exoskeleton is similar across all pavements. Conclusion. The compressive Knee-Ankle/SD capacity of the pavement and the unevenness of the pavement are important factors that influence interjoint coordination, which can be used as key control elements of gait to adapt different pavements for robotic exoskeleton. Novelty. We provide a basis of parameter change of kinematics on different common grounds for the design and optimization of robotic exoskeleton for motor recovery. 1. Introduction classification and algorithm of gait control [2] for robotic exoskeleton. The robotic exoskeleton reduces the muscular The robotic exoskeleton provides assistance in time and effort compared to free walking [3, 4]. To increase walking replicates human walking at some extent. The interjoint efficiency of humans, it needs to reduce impact on the coordination patterns of human walking are applied to the natural walking gait by minimizing changes in kinematics gait control for robotic exoskeleton. However, the gait of [5]. In addition, the appropriate assistive strategies consti- robotic exoskeleton for rehabilitation is usually fixed, and tute the human-robot motion, which benefits the assistive the robotic exoskeleton for rehabilitation cannot perceive isotropy of the motion, and improves the assistive effi- ground changes. Although much is known about the ciency of the force [6]. Matching the assistance pattern intersegmental coordination of walking on the treadmill or of exoskeleton with the individual also needs to maximize uneven ground [1], the effect of common grounds such as the advantage of the device and minimize the human the tiled ground on interjoint coordination has not been energy cost during walking [7]. studied systematically. The interjoint coordination in a sagittal plane was The information of walking patterns, such as the coor- analyzed by the continuous relative phase (CRP) [8], which dination pattern between joints, provides basic data to correlated temporal-spatial parameters [9] in joints and was 2 Applied Bionics and Biomechanics (a) (b) (c) Figure 1: Experimental environment: (a) participant with exoskeleton walking on tiled pavement, (b) participant without exoskeleton walking on pebbled pavement, and (c) tiled pavement, carpet pavement, wooden pavement, concrete pavement, and pebbled pavement. used to evaluate the intersegment coordination [1, 10–12] as study of consistent proximal-to-distal coordination to pro- well as the interjoint coordination [8, 13, 14]. Human walk- vide support for the motion planning of robotic exoskeleton ing on different kinds of grounds seems to adopt different during walking on different kinds of grounds. The hypotheses walking patterns through adjusting the joint kinematic. Still, of this study are as follows: the coordination patterns of a human body with exoskeletons Hypothesis 1: when walking with exoskeletons on the normally imitate the coordination patterns of the human five kinds of pavements, the pattern and variability of body without exoskeletons. The more similar the interjoint interjoint coordination would be similar between different coordination patterns of robotic exoskeleton is to that of a pavements normal person, the better for hemiplegic patients on motor Hypothesis 2: when walking without exoskeletons on recovery. It will be detrimental to the rehabilitation of hemi- the five kinds of pavements, there would be a significant plegic patients if the tendency of the joint angle of the human difference between different pavements in the pattern and body with/without exoskeleton is so different. Robotic lower variability of interjoint coordination limb exoskeletons have significant potential for gait assis- tance and rehabilitation [15]. However, we partly understand 2. Methods how people walking with robotic devices adapt to the daily living environment. Studying how an individual adapts or Eight young and healthy participants (age: 23 ± 1:6 years, sex: responds to different grounds in walking remains an open male, leg length: 0:89 ± 0:03 m, mass: 76:6±6:4kg, and challenge [16, 17]. height: 172:6±6:5cm) were recruited to take part in the What is more, it is hard to find studies focusing on the experiment with written informed consent before the effect of common grounds on joint kinematics when humans experiment. All procedures were approved by the Sichuan walk on different kinds of grounds with exoskeleton in daily Provincial Rehabilitation Hospital Review Board. life. Hence, in the current study, five kinds of pavements The kinematics data were captured by the VICON (tiled pavement, carpet pavement, wooden pavement, System (V5, Oxford, VICON, UK) with 8 infrared cameras concrete pavement, and pebble pavement) were paved with at 100 Hz. The human-exoskeleton system marker set real material in the experimental environment to figure out (Figure 1(a)) was a modification of a marker set in the which joint the humans would adjust to adapt different VICON system. The human and exoskeleton were regarded pavements and to see if they adjust the patterns of joint kine- as a whole system in the modification of the marker set, so matics to adapt different kinds of grounds. Based on CRP, the markers placed on the human’s pelvis, legs, ankles, and heels consistent proximal-to-distal coordination, such as hip-knee are moved to the exoskeleton’s pelvis, legs, ankles, and heels. coordination and knee-ankle coordination, was measured Thirty-nine reflective markers were placed on the human- with/without exoskeleton on five kinds of pavements across exoskeleton system, including the seventh cervical vertebrae, eight healthy participants in this study. We also expect the sternum, shoulders, elbows, anterior-superior iliac spine, Applied Bionics and Biomechanics 3 Table 1: Friction coefficients of pavements. Pavements Tiled Carpet Wooden Concrete Pebbled Coefficient of frictions 0.32 0.15 0.33 0.34 0.20 Table 2: Gait parameters with/without exoskeleton at five kinds of pavements. With exoskeleton Without exoskeleton Tiled Carpet Wooden Concrete Pebbled Tiled Carpet Wooden Concrete Pebbled 9±5 9 ±4 6±5 6 ±6 8±4 14±3 13±5 14 ± 4 14±2 12 ± 8 Peak ankle dorsiflexion in midstance ( ) Peak ankle plantar flexion in late stance ()N N N N N 9±8 10±7 9 ±7 7±8 3 ±7 10 ±5 10 ±4 10 ± 12 8 ±6 9±5 6 ±5 7±6 6 ±5 6±6 9 ±8 Peak ankle dorsiflexion in swing ( ) 34 ± 1 34 ± 1 21 ± 18 26 ± 16 34 ± 1 34 ± 11 31 ± 9 31 ± 8 31 ± 8 23 ± 16 Peak knee flexion in swing ( ) 4± 2 4 ±2 2± 2 3 ±3 3±2 9 ±6 10 ±7 8±6 8 ±7 6±7 Peak hip extension in late stance ( ) 34 ± 1 34 ± 1 21 ± 18 26 ± 16 34 ± 1 34 ± 11 31 ± 9 31 ± 8 31 ± 8 23 ± 16 Peak hip flexion in swing ( ) Peak values as the mean ± standard deviation; N: no data. exoskeleton thighs, exoskeleton knees, exoskeleton shanks, the normalized angular velocity to the normalized angular nd exoskeleton ankles, 2 metatarsal heads, and exoskeleton displacement, and CRP is equal to the phase angle of the heels. In addition, four markers were stuck on the headband proximal joint minus the phase angle of the distal joint and two markers were stuck on the wristband. [9, 11, 14]. The root mean square of CRP (CRP ) was RMS The lower limb exoskeleton called AIDER (Figure 1(a)) is selected to analyze the magnitude of dephasing between developed by our lab, which can assist walking for T7-T12 joints at a specific phase of the gait cycle, and the standard SCI patients with a height of 160-185 cm. The main control- deviation of CRP (CRP ) was selected to assess the variabil- SD ler and battery are set on the back. Two motors are, respec- ity of the coordination pattern between joints in the full gait tively, fixed on the unilateral hip joint and the knee joint to cycle [9]. Peak ankle dorsiflexion in the midstance, peak provide active drives, and one spring is fixed on the ankle ankle plantar flexion in the late stance, peak ankle dorsiflex- joint to provide passive drives. Two adjustable crutches with ion in swing, peak knee flexion in swing, peak hip extension two keys interacting with the main controller wirelessly assist in the late stance, and peak hip flexion in swing were selected the balance of the human-exoskeleton system. The interfaces as six key parameters for the kinematic analysis. All data were between AIDER and the participant’s body are two foot bind- processed by MATLAB (MathWorks, Natick, MA, USA). To ings, two bands tied to the front protection pad to constraint examine the changes in kinematics across one gait cycle for the calf, two bands tied to the back protection pad to ankle, knee, and hip joints, the paired t-test was used to ana- constraint the thigh, and two buckled waist belts limiting lyze the statistical significance of gait parameters between the upper body in it. AIDER (8 degrees of freedom, 26 kg) pavements by SPSS (v25, IBM Corp., Armonk, USA). The allows patients to walk at the speed of 0.03 m/s-0.9 m/s. value of significance level was set at an alpha value of 0.05. Five typical pavements (Figure 1(c)) are made of real materials. The sizes of all simulated surfaces with different 3. Results friction coefficients (Table 1) are 3 m by 1 m. Pavements were tiled pavement, carpet pavement, wooden pavement, 3.1. Joint Kinematics. In a gait cycle, the trends of hip, knee, concrete pavement, and pebble pavement. Participants first and ankle angles of the human system are not exactly the walked without exoskeleton on the ranked pavements for same as normal people. The overall angle of the hip, knee, 2 meters for 4 times at normal speed, and then, they and ankle joints of the human-machine system is much walked with exoskeleton on the pavements at normal speed smaller than that of a normal person. Peak ankle dorsiflexion for 2 meters for 4 times after at least 1-hour training. To with exoskeleton in the midstance phase is larger than that ensure the safety of participants, a researcher followed the without exoskeleton on five kinds of pavements (Table 2). participants’ walking with exoskeleton throughout the whole With exoskeleton, there is a significant difference in the peak experiment. ankle dorsiflexion in the midstance between the carpet pave- The gait cycle from heel strike to heel strike was deter- ment and the pebble pavement (paired t-tests, p =0:009). mined by the trajectory of heel markers. All variables were Without exoskeleton, the peak ankle plantar flexion (paired normalized from 0 to 1, compared with a stride cycle. Each t-tests, p =0:031) in the late stance phase has a significant joint’s angle in a sagittal plane was interpolated to the same difference between the pebble pavement and the carpet pave- quantity in one gait cycle. The angular velocity of each joint ment. Similarly, without exoskeleton, the peak ankle plantar was derived from the differentiation of angle displacement. flexion (paired t-tests, p =0:043) in the late stance phase The phase angle is equal to the arctangent of the ratio of has a significant difference between the pebble pavement 4 Applied Bionics and Biomechanics With exoskeleton Without exoskeleton 20 20 ES MS LS SW ES MS LS SW 15 15 10 10 5 5 0 0 –5 –5 –10 –10 0 102030405060708090 100 0 102030405060708090 100 60 70 ES MS LS SW ES MS LS SW 50 60 40 50 30 40 20 30 10 20 0 10 –10 0 0 102030405060708090 100 0 102030405060708090 100 40 40 ES MS LS SW ES MS LS SW 30 30 20 20 10 10 0 0 –10 –10 0 102030405060708090 100 0 102030405060708090 100 Gait cycle (%) Gait cycle (%) Tiled Concrete Carpet Pebbled Wooden Figure 2: Changes in kinematics at the ankle, knee, and hip. Mean angle of the ankle, knee, and hip in a sagittal plane for participants (n =8) with/without exoskeleton over the gait cycle on each kind of pavements. The gait cycle is from the heel strike to the next heel strike of the left foot. ES = early stance; MS = midstance; LS = late stance; SW = swing phase. and the wooden pavement. The ungiven results of paired ankle angle without exoskeleton over the gait cycle on the t-test of peak values with/without exoskeleton between pebble pavement is the largest among the five kinds of pave- pavements indicate no significant difference. ments. With/without exoskeleton, the knee angle in the On five types of pavements, the trends (see Figure 2) of stance phase tends to be consistent on the five kinds of pave- the joint angle of the human-exoskeleton system are signifi- ments. On the contrary, the knee angle in the stance phase cantly different from the trends of the joint angle without with/without exoskeleton tends to be different in the five exoskeleton. The ankle angle with exoskeleton over the gait kinds of pavements. Although the hip angle with exoskeleton cycle (except the early stance phase) on the pebble pavement in the stance phase on the pebble pavement is almost larger is the smallest among the five kinds of pavements, but the than that on the other pavements, the hip angle with Hip angle (°) Knee angle (°) Ankle angle (°) Applied Bionics and Biomechanics 5 With exoskeleton Without exoskeleton 200 200 ES MS LS SW ES MS LS SW 50 0 –50 –100 –50 –150 –100 –200 0 20 40 60 80 100 0 20 40 60 80 100 100 100 ES MS LS SW ES MS LS SW 50 50 0 0 –50 –50 –100 –100 –150 –150 –200 -200 0 20 40 60 80 100 0 20 40 60 80 100 Gait cycle (%) Gait cycle (%) Tiled Concrete Carpet Pebbled Wooden Figure 3: Continuous relative phase (CRP) patterns between the knee and ankle and between the hip and knee in the sagittal plane. Mean CRP for participants (n =8) with/without exoskeleton over the gait cycle on each kind of pavements. The gait cycle is from the heel strike to the next heel strike of the left foot. ES = early stance; MS = midstance; LS = late stance; SW = swing phase. exoskeleton in the first half of the swing phase on the pebble exoskeleton, while the hip precedes the knee in the late stance pavement is smaller than the hip angle with exoskeleton on phase on all pavements without exoskeleton. the other pavements. This trend is similar to the hip angle The CRP on the pebble pavement with exo- Hip-Knee/RMS without exoskeleton. skeleton is larger than that on the other pavements in the early stance phase and in the midstance phase. On the con- 3.2. Measurement of Interjoint Coordination. This study trary, the CRP on pebbled pavement without Hip-Knee/RMS explored the effects of different pavements on coordination exoskeleton is less than that on the other pavements in all patterns, using the root mean square of CRP. RMS values phases, while the CRP on the tiled pavement Hip-Knee/RMS indicate the magnitude of the dephasing between two adja- without exoskeleton is less than that on the other pavements cent joints but not on which joint precedes [12]. However, in all phases (as seen in Table 3). With exoskeleton, the the CRP curves (Figure 3) provide which joint precedes on CRP in the midstance phase has a significant Hip-Knee/RMS the specific pavement with/without exoskeleton: the knee difference between the carpet pavement and the wooden precedes the ankle at all phases of the gait cycle on pavements pavement (paired t-tests, p =0:034), between the carpet (except the pebble pavement in the swing phase) with exo- pavement and the concrete pavement (paired t-tests, p = skeleton, and the hip precedes the knee in the stance phase 0:028), and between the carpet pavement and the pebble on all pavements with exoskeleton. The knee precedes the pavement (paired t-tests, p =0:044). Moreover, the ankle in the midstance phases on pavements without exo- CRP with exoskeleton in the late stance phase Hip-Knee/RMS skeleton, and the ankle precedes the knee in the early stance has a significant difference between the wooden pavement phase on pavements (except the carpet pavement) without and the pebble pavement (paired t-tests, p =0:029) and in the exoskeleton. The knee precedes the hip in the early stance swing phase between the carpet pavement and the wooden phase and in the midstance phase on all pavements without pavement (paired t-tests, p =0:024). Without exoskeleton, CRP (°) CRP (°) Hip-Knee Knee-Ankle 6 Applied Bionics and Biomechanics Table 3: Coordination: CRP root mean square (CRP ) and variability (CRP ) over the full gait cycle for participants (n =8) with/without RMS SD exoskeleton over the gait cycle on each kind of pavements. With exoskeleton Without exoskeleton Tiled Carpet Wooden Concrete Pebbled Tiled Carpet Wooden Concrete Pebbled CRP Hip-Knee/RMS 148 ± 33 155 ± 18 158 ± 22 161 ± 27 162 ± 15 139 ± 20 313 ± 20 133 ± 30 130 ± 21 107 ± 37 Early stance 55 ± 27 53 ± 20 67 ± 30 77 ± 31 83 ± 31 82 ± 25 79 ± 22 79 ± 17 80 ± 21 52 ± 35 Midstance 6 ± 8 5 ± 5 1 ± 1 4 ± 6 2 ± 1 62 ± 21 56 ± 14 56 ± 10 58 ± 20 44 ± 20 Late stance 34 ± 7 38 ± 6 34 ± 7 35 ± 8 33 ± 7 74 ± 5 71 ± 9 73 ± 11 72 ± 8 71 ± 9 Swing CRP Knee-Ankle/RMS 82 ± 63 86 ± 59 77 ± 61 56 ± 58 50 ± 47 38 ± 47 42 ± 26 40 ± 33 28 ± 13 29 ± 14 Early stance Midstance 148 ± 50 149 ± 47 147 ± 39 141 ± 59 136 ± 57 120 ± 14 133 ± 13 125 ± 17 123 ± 15 130 ± 11 138 ± 60 129 ± 52 166 ± 13 146 ± 50 151 ± 58 87 ± 41 90 ± 20 93 ± 25 86 ± 27 112 ± 32 Late stance Swing 58 ± 30 50 ± 24 70 ± 11 71 ± 26 82 ± 28 75 ± 11 74 ± 12 74 ± 13 72 ± 28 59 ± 20 55 ± 13 57 ± 9 60 ± 11 63 ± 11 65 ± 10 75 ± 6 71 ± 7 71 ± 8 71 ± 9 63 ± 9 CRP Hip-Knee/SD 64 ± 16 64 ± 16 71 ± 5 63 ± 21 67 ± 13 89 ± 8 90 ± 8 89 ± 9 87 ± 15 84 ± 11 CRP Knee-Ankle/SD Root mean square (RMS) as the mean ± standard deviation.(0–10%) data points in one gait cycle for each participant, (10–50%) data points in one gait cycle for midstance, (50–60%) data points in one gait cycle for late stance, and (60–100%) data points in one gait cycle for the swing phase. the CRP in the early stance phase has a signifi- and in the late stance phase between the concrete pavement Hip-Knee/RMS cant difference between the tiled pavement and the concrete and the pebble pavement (paired t-tests, p =0:048). pavement (paired t-tests, p =0:02) and between the wooden With exoskeleton, there is a significant difference of the pavement and the pebble pavement (paired t-tests, p = CRP between the carpet pavement and the wooden Hip-Knee/SD 0:009). In addition, the CRP without exoskeleton pavement (paired t-tests, p =0:024) in the full gait cycle. Hip-Knee/RMS in the late stance phase has a significant difference between Without exoskeleton, there is a significant difference of the the carpet pavement and the pebble pavement (paired CRP in the full gait cycle between the tiled pave- Hip-Knee/SD t-tests, p =0:033) and between the concrete pavement ment and the concrete pavement (paired t-tests, p =0:029), and the pebble pavement (paired t-tests, p =0:033). between the tiled pavement and the pebble pavement (paired The CRP on the tiled pavement with exo- t-tests, p =0:033), between the carpet pavement and the peb- Knee-Ankle/RMS skeleton is larger than that on the other pavements in the ble pavement (paired t-tests, p =0:015), and between the early stance phase and in the midstance phase, while the wooden pavement and the pebble pavement (paired t-tests, CRP on the tiled pavement with exoskeleton is p =0:005). The trends of CRP with exoskeleton oscillate Knee-Ankle/RMS the less than that on the other pavements in the late stance more frequently than the trends of CRP without exoskeleton phase and in the swing phase. On the contrary, the over the gait cycle on the pavements. CRP on the pebble pavement with exoskeleton Knee-Ankle/RMS is the less than that on the other pavements in the early 4. Discussion stance phase and in the midstance phase, while the CRP on the tiled pavement with exoskeleton Our results suggest that the common pavements cause a sig- Knee-Ankle/RMS is larger than that on the other pavements in the late stance nificant difference of interjoint coordination with/without phase and in the swing phase. The CRP on the exoskeleton only in some phases of the gait cycle, so the Knee-Ankle/RMS pebble pavement without exoskeleton is less than that on hypothesis 1 and the hypothesis 2 are only partially proved. the other pavements in the early stance phase and in the The compressive capacity of the carpet pavement is obviously swing phase, while the CRP on the tiled pave- lower than the other pavements, which may cause the dif- Knee-Ankle/RMS ment without exoskeleton is larger than that on the other ference of CRP with exoskeleton between the Hip-Knee/RMS pavements in the midstance phase and late stance phase. carpet pavement and other pavements (except the tiled The CRP on the carpet pavement without exo- pavement) in the midstance. Moreover, the compressive Knee-Ankle/RMS skeleton is larger than that on the other pavements in the capacity of the carpet pavement may cause the difference early stance phase and in the midstance phase (as seen in of CRP with exoskeleton between the carpet Knee-Ankle/RMS Table 3). With exoskeleton, there is a significant difference pavement and the pebble pavement in the late stance of the CRP between the carpet pavement and phase and in the swing phase. However, the unevenness Knee-Ankle/RMS the pebble pavement in the late stance phase (paired t-tests, of pebble pavement as another influencing factor should p =0:027) and in the swing phase (paired t-tests, p =0:026). not be ignored. Because the unevenness of the pebble Without exoskeleton, there is a significant difference of the pavement increases the physical energy consumption CRP in the midstance phase between the tiled [18], the CRP of the pebble pavement without Knee-Ankle/RMS Hip-Knee/RMS pavement and the carpet pavement (paired t-tests, p =0:01) exoskeleton is lower than the other pavements and Applied Bionics and Biomechanics 7 statistically different from the carpet pavement and the con- ment kinematics have not been included. Second, there are crete pavement. The unevenness of the pebble pavement may not only random displacements between the human body induce the cautious dynamic neuromuscular control [13] of and the exoskeleton but also individual differences between participants and enhance their leg stiffness [1, 10] so that human bodies, which make it difficult for the human- the CRP of the pebble pavement without exoskel- exoskeleton model to measure the exact gait parameters of Hip-Knee/SD eton is smaller than that of other pavements and statistically human-exoskeleton. Therefore, in exoskeleton experiments, different from that of other pavements (except concrete there are uncertain errors in the gait parameters of human- pavement). When walking on pavements with exoskeleton, exoskeleton. Third, this study did not explore muscle adapta- participants need to adjust the center of gravity to keep the tion and joint kinetics of people who may adapt to different human-exoskeleton system balance with the help of crutches friction coefficients. Future work will focus on the effects of and prepare for the next step in stance, which may cause the different friction coefficient pavements on muscle adaptation difference of interjoint coordination patterns with exoskeleton and joint dynamics, which can further explain how people between pavements. adapt to pavements with different coefficients of friction. The exoskeleton was set in a fixed gait and joint moment, so the peak values should be similar between pavements. Data Availability However, the peak ankle dorsiflexion of walking on the car- pet pavement in the midstance is significantly different from The data that support the findings of this study are available that of walking on the pebble pavement, which may due to on request from the corresponding author, Jing Qiu. the active intervention from participants on the ankle. When the participants without exoskeleton walk on the pavements, Conflicts of Interest it is only found that the peak ankle plantar flexion in the late stance phase on the pebble pavement is significantly different The authors declare that they have no conflicts of interest. from that on the carpet pavement and the wooden pavement. This result indicates that the friction coefficients of Acknowledgments pavements do not impose on gait parameters in kinematics, but the unevenness of pavements obviously affects the gait This research was supported by the Fundamental Research parameters in kinematics [1, 10]. 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Effect of Common Pavements on Interjoint Coordination of Walking with and without Robotic Exoskeleton

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Copyright © 2019 Jinlei Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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10.1155/2019/5823908
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Hindawi Applied Bionics and Biomechanics Volume 2019, Article ID 5823908, 8 pages https://doi.org/10.1155/2019/5823908 Research Article Effect of Common Pavements on Interjoint Coordination of Walking with and without Robotic Exoskeleton 1 2 2 2 1 Jinlei Wang, Jing Qiu , Lei Hou, Xiaojuan Zheng, and Suihuai Yu Northwestern Polytechnical University, China University of Electronic Science and Technology of China, China Correspondence should be addressed to Jing Qiu; qiujing@uestc.edu.cn Received 22 March 2019; Revised 23 July 2019; Accepted 2 September 2019; Published 1 October 2019 Guest Editor: Michelle Johnson Copyright © 2019 Jinlei Wang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. The analysis and comprehension of the coordination control of a human gait on common grounds benefit the development of robotic exoskeleton for motor recovery. Objective. This study investigated whether the common grounds effect the interjoint coordination of healthy participants with/without exoskeletons in walking. Methods. The knee-ankle coordination and hip-knee coordination of 8 healthy participants in a sagittal plane were measured on five kinds of pavements (tiled, carpet, wooden, concrete, and pebbled) with/without exoskeletons, using the continuous relative phase (CRP). The root mean square of CRP (CRP ) over each phase of the gait cycle is used to analyze the magnitude of dephasing between joints, and the standard RMS deviation of CRP (CRP ) in the full gait cycle is used to assess the variability of coordination patterns between joints. SD Results. The CRP of the carpet pavement with exoskeleton is different from that of other pavements (except the Hip-Knee/RMS tiled pavement) in the midstance phase. The CRP on the pebble pavement without exoskeleton is less than that Hip-Knee/RMS on the other pavements in all phases. The CRP of the pebble pavement without exoskeleton is smaller than that Hip-Knee/SD of other pavements. The CRP with/without exoskeleton is similar across all pavements. Conclusion. The compressive Knee-Ankle/SD capacity of the pavement and the unevenness of the pavement are important factors that influence interjoint coordination, which can be used as key control elements of gait to adapt different pavements for robotic exoskeleton. Novelty. We provide a basis of parameter change of kinematics on different common grounds for the design and optimization of robotic exoskeleton for motor recovery. 1. Introduction classification and algorithm of gait control [2] for robotic exoskeleton. The robotic exoskeleton reduces the muscular The robotic exoskeleton provides assistance in time and effort compared to free walking [3, 4]. To increase walking replicates human walking at some extent. The interjoint efficiency of humans, it needs to reduce impact on the coordination patterns of human walking are applied to the natural walking gait by minimizing changes in kinematics gait control for robotic exoskeleton. However, the gait of [5]. In addition, the appropriate assistive strategies consti- robotic exoskeleton for rehabilitation is usually fixed, and tute the human-robot motion, which benefits the assistive the robotic exoskeleton for rehabilitation cannot perceive isotropy of the motion, and improves the assistive effi- ground changes. Although much is known about the ciency of the force [6]. Matching the assistance pattern intersegmental coordination of walking on the treadmill or of exoskeleton with the individual also needs to maximize uneven ground [1], the effect of common grounds such as the advantage of the device and minimize the human the tiled ground on interjoint coordination has not been energy cost during walking [7]. studied systematically. The interjoint coordination in a sagittal plane was The information of walking patterns, such as the coor- analyzed by the continuous relative phase (CRP) [8], which dination pattern between joints, provides basic data to correlated temporal-spatial parameters [9] in joints and was 2 Applied Bionics and Biomechanics (a) (b) (c) Figure 1: Experimental environment: (a) participant with exoskeleton walking on tiled pavement, (b) participant without exoskeleton walking on pebbled pavement, and (c) tiled pavement, carpet pavement, wooden pavement, concrete pavement, and pebbled pavement. used to evaluate the intersegment coordination [1, 10–12] as study of consistent proximal-to-distal coordination to pro- well as the interjoint coordination [8, 13, 14]. Human walk- vide support for the motion planning of robotic exoskeleton ing on different kinds of grounds seems to adopt different during walking on different kinds of grounds. The hypotheses walking patterns through adjusting the joint kinematic. Still, of this study are as follows: the coordination patterns of a human body with exoskeletons Hypothesis 1: when walking with exoskeletons on the normally imitate the coordination patterns of the human five kinds of pavements, the pattern and variability of body without exoskeletons. The more similar the interjoint interjoint coordination would be similar between different coordination patterns of robotic exoskeleton is to that of a pavements normal person, the better for hemiplegic patients on motor Hypothesis 2: when walking without exoskeletons on recovery. It will be detrimental to the rehabilitation of hemi- the five kinds of pavements, there would be a significant plegic patients if the tendency of the joint angle of the human difference between different pavements in the pattern and body with/without exoskeleton is so different. Robotic lower variability of interjoint coordination limb exoskeletons have significant potential for gait assis- tance and rehabilitation [15]. However, we partly understand 2. Methods how people walking with robotic devices adapt to the daily living environment. Studying how an individual adapts or Eight young and healthy participants (age: 23 ± 1:6 years, sex: responds to different grounds in walking remains an open male, leg length: 0:89 ± 0:03 m, mass: 76:6±6:4kg, and challenge [16, 17]. height: 172:6±6:5cm) were recruited to take part in the What is more, it is hard to find studies focusing on the experiment with written informed consent before the effect of common grounds on joint kinematics when humans experiment. All procedures were approved by the Sichuan walk on different kinds of grounds with exoskeleton in daily Provincial Rehabilitation Hospital Review Board. life. Hence, in the current study, five kinds of pavements The kinematics data were captured by the VICON (tiled pavement, carpet pavement, wooden pavement, System (V5, Oxford, VICON, UK) with 8 infrared cameras concrete pavement, and pebble pavement) were paved with at 100 Hz. The human-exoskeleton system marker set real material in the experimental environment to figure out (Figure 1(a)) was a modification of a marker set in the which joint the humans would adjust to adapt different VICON system. The human and exoskeleton were regarded pavements and to see if they adjust the patterns of joint kine- as a whole system in the modification of the marker set, so matics to adapt different kinds of grounds. Based on CRP, the markers placed on the human’s pelvis, legs, ankles, and heels consistent proximal-to-distal coordination, such as hip-knee are moved to the exoskeleton’s pelvis, legs, ankles, and heels. coordination and knee-ankle coordination, was measured Thirty-nine reflective markers were placed on the human- with/without exoskeleton on five kinds of pavements across exoskeleton system, including the seventh cervical vertebrae, eight healthy participants in this study. We also expect the sternum, shoulders, elbows, anterior-superior iliac spine, Applied Bionics and Biomechanics 3 Table 1: Friction coefficients of pavements. Pavements Tiled Carpet Wooden Concrete Pebbled Coefficient of frictions 0.32 0.15 0.33 0.34 0.20 Table 2: Gait parameters with/without exoskeleton at five kinds of pavements. With exoskeleton Without exoskeleton Tiled Carpet Wooden Concrete Pebbled Tiled Carpet Wooden Concrete Pebbled 9±5 9 ±4 6±5 6 ±6 8±4 14±3 13±5 14 ± 4 14±2 12 ± 8 Peak ankle dorsiflexion in midstance ( ) Peak ankle plantar flexion in late stance ()N N N N N 9±8 10±7 9 ±7 7±8 3 ±7 10 ±5 10 ±4 10 ± 12 8 ±6 9±5 6 ±5 7±6 6 ±5 6±6 9 ±8 Peak ankle dorsiflexion in swing ( ) 34 ± 1 34 ± 1 21 ± 18 26 ± 16 34 ± 1 34 ± 11 31 ± 9 31 ± 8 31 ± 8 23 ± 16 Peak knee flexion in swing ( ) 4± 2 4 ±2 2± 2 3 ±3 3±2 9 ±6 10 ±7 8±6 8 ±7 6±7 Peak hip extension in late stance ( ) 34 ± 1 34 ± 1 21 ± 18 26 ± 16 34 ± 1 34 ± 11 31 ± 9 31 ± 8 31 ± 8 23 ± 16 Peak hip flexion in swing ( ) Peak values as the mean ± standard deviation; N: no data. exoskeleton thighs, exoskeleton knees, exoskeleton shanks, the normalized angular velocity to the normalized angular nd exoskeleton ankles, 2 metatarsal heads, and exoskeleton displacement, and CRP is equal to the phase angle of the heels. In addition, four markers were stuck on the headband proximal joint minus the phase angle of the distal joint and two markers were stuck on the wristband. [9, 11, 14]. The root mean square of CRP (CRP ) was RMS The lower limb exoskeleton called AIDER (Figure 1(a)) is selected to analyze the magnitude of dephasing between developed by our lab, which can assist walking for T7-T12 joints at a specific phase of the gait cycle, and the standard SCI patients with a height of 160-185 cm. The main control- deviation of CRP (CRP ) was selected to assess the variabil- SD ler and battery are set on the back. Two motors are, respec- ity of the coordination pattern between joints in the full gait tively, fixed on the unilateral hip joint and the knee joint to cycle [9]. Peak ankle dorsiflexion in the midstance, peak provide active drives, and one spring is fixed on the ankle ankle plantar flexion in the late stance, peak ankle dorsiflex- joint to provide passive drives. Two adjustable crutches with ion in swing, peak knee flexion in swing, peak hip extension two keys interacting with the main controller wirelessly assist in the late stance, and peak hip flexion in swing were selected the balance of the human-exoskeleton system. The interfaces as six key parameters for the kinematic analysis. All data were between AIDER and the participant’s body are two foot bind- processed by MATLAB (MathWorks, Natick, MA, USA). To ings, two bands tied to the front protection pad to constraint examine the changes in kinematics across one gait cycle for the calf, two bands tied to the back protection pad to ankle, knee, and hip joints, the paired t-test was used to ana- constraint the thigh, and two buckled waist belts limiting lyze the statistical significance of gait parameters between the upper body in it. AIDER (8 degrees of freedom, 26 kg) pavements by SPSS (v25, IBM Corp., Armonk, USA). The allows patients to walk at the speed of 0.03 m/s-0.9 m/s. value of significance level was set at an alpha value of 0.05. Five typical pavements (Figure 1(c)) are made of real materials. The sizes of all simulated surfaces with different 3. Results friction coefficients (Table 1) are 3 m by 1 m. Pavements were tiled pavement, carpet pavement, wooden pavement, 3.1. Joint Kinematics. In a gait cycle, the trends of hip, knee, concrete pavement, and pebble pavement. Participants first and ankle angles of the human system are not exactly the walked without exoskeleton on the ranked pavements for same as normal people. The overall angle of the hip, knee, 2 meters for 4 times at normal speed, and then, they and ankle joints of the human-machine system is much walked with exoskeleton on the pavements at normal speed smaller than that of a normal person. Peak ankle dorsiflexion for 2 meters for 4 times after at least 1-hour training. To with exoskeleton in the midstance phase is larger than that ensure the safety of participants, a researcher followed the without exoskeleton on five kinds of pavements (Table 2). participants’ walking with exoskeleton throughout the whole With exoskeleton, there is a significant difference in the peak experiment. ankle dorsiflexion in the midstance between the carpet pave- The gait cycle from heel strike to heel strike was deter- ment and the pebble pavement (paired t-tests, p =0:009). mined by the trajectory of heel markers. All variables were Without exoskeleton, the peak ankle plantar flexion (paired normalized from 0 to 1, compared with a stride cycle. Each t-tests, p =0:031) in the late stance phase has a significant joint’s angle in a sagittal plane was interpolated to the same difference between the pebble pavement and the carpet pave- quantity in one gait cycle. The angular velocity of each joint ment. Similarly, without exoskeleton, the peak ankle plantar was derived from the differentiation of angle displacement. flexion (paired t-tests, p =0:043) in the late stance phase The phase angle is equal to the arctangent of the ratio of has a significant difference between the pebble pavement 4 Applied Bionics and Biomechanics With exoskeleton Without exoskeleton 20 20 ES MS LS SW ES MS LS SW 15 15 10 10 5 5 0 0 –5 –5 –10 –10 0 102030405060708090 100 0 102030405060708090 100 60 70 ES MS LS SW ES MS LS SW 50 60 40 50 30 40 20 30 10 20 0 10 –10 0 0 102030405060708090 100 0 102030405060708090 100 40 40 ES MS LS SW ES MS LS SW 30 30 20 20 10 10 0 0 –10 –10 0 102030405060708090 100 0 102030405060708090 100 Gait cycle (%) Gait cycle (%) Tiled Concrete Carpet Pebbled Wooden Figure 2: Changes in kinematics at the ankle, knee, and hip. Mean angle of the ankle, knee, and hip in a sagittal plane for participants (n =8) with/without exoskeleton over the gait cycle on each kind of pavements. The gait cycle is from the heel strike to the next heel strike of the left foot. ES = early stance; MS = midstance; LS = late stance; SW = swing phase. and the wooden pavement. The ungiven results of paired ankle angle without exoskeleton over the gait cycle on the t-test of peak values with/without exoskeleton between pebble pavement is the largest among the five kinds of pave- pavements indicate no significant difference. ments. With/without exoskeleton, the knee angle in the On five types of pavements, the trends (see Figure 2) of stance phase tends to be consistent on the five kinds of pave- the joint angle of the human-exoskeleton system are signifi- ments. On the contrary, the knee angle in the stance phase cantly different from the trends of the joint angle without with/without exoskeleton tends to be different in the five exoskeleton. The ankle angle with exoskeleton over the gait kinds of pavements. Although the hip angle with exoskeleton cycle (except the early stance phase) on the pebble pavement in the stance phase on the pebble pavement is almost larger is the smallest among the five kinds of pavements, but the than that on the other pavements, the hip angle with Hip angle (°) Knee angle (°) Ankle angle (°) Applied Bionics and Biomechanics 5 With exoskeleton Without exoskeleton 200 200 ES MS LS SW ES MS LS SW 50 0 –50 –100 –50 –150 –100 –200 0 20 40 60 80 100 0 20 40 60 80 100 100 100 ES MS LS SW ES MS LS SW 50 50 0 0 –50 –50 –100 –100 –150 –150 –200 -200 0 20 40 60 80 100 0 20 40 60 80 100 Gait cycle (%) Gait cycle (%) Tiled Concrete Carpet Pebbled Wooden Figure 3: Continuous relative phase (CRP) patterns between the knee and ankle and between the hip and knee in the sagittal plane. Mean CRP for participants (n =8) with/without exoskeleton over the gait cycle on each kind of pavements. The gait cycle is from the heel strike to the next heel strike of the left foot. ES = early stance; MS = midstance; LS = late stance; SW = swing phase. exoskeleton in the first half of the swing phase on the pebble exoskeleton, while the hip precedes the knee in the late stance pavement is smaller than the hip angle with exoskeleton on phase on all pavements without exoskeleton. the other pavements. This trend is similar to the hip angle The CRP on the pebble pavement with exo- Hip-Knee/RMS without exoskeleton. skeleton is larger than that on the other pavements in the early stance phase and in the midstance phase. On the con- 3.2. Measurement of Interjoint Coordination. This study trary, the CRP on pebbled pavement without Hip-Knee/RMS explored the effects of different pavements on coordination exoskeleton is less than that on the other pavements in all patterns, using the root mean square of CRP. RMS values phases, while the CRP on the tiled pavement Hip-Knee/RMS indicate the magnitude of the dephasing between two adja- without exoskeleton is less than that on the other pavements cent joints but not on which joint precedes [12]. However, in all phases (as seen in Table 3). With exoskeleton, the the CRP curves (Figure 3) provide which joint precedes on CRP in the midstance phase has a significant Hip-Knee/RMS the specific pavement with/without exoskeleton: the knee difference between the carpet pavement and the wooden precedes the ankle at all phases of the gait cycle on pavements pavement (paired t-tests, p =0:034), between the carpet (except the pebble pavement in the swing phase) with exo- pavement and the concrete pavement (paired t-tests, p = skeleton, and the hip precedes the knee in the stance phase 0:028), and between the carpet pavement and the pebble on all pavements with exoskeleton. The knee precedes the pavement (paired t-tests, p =0:044). Moreover, the ankle in the midstance phases on pavements without exo- CRP with exoskeleton in the late stance phase Hip-Knee/RMS skeleton, and the ankle precedes the knee in the early stance has a significant difference between the wooden pavement phase on pavements (except the carpet pavement) without and the pebble pavement (paired t-tests, p =0:029) and in the exoskeleton. The knee precedes the hip in the early stance swing phase between the carpet pavement and the wooden phase and in the midstance phase on all pavements without pavement (paired t-tests, p =0:024). Without exoskeleton, CRP (°) CRP (°) Hip-Knee Knee-Ankle 6 Applied Bionics and Biomechanics Table 3: Coordination: CRP root mean square (CRP ) and variability (CRP ) over the full gait cycle for participants (n =8) with/without RMS SD exoskeleton over the gait cycle on each kind of pavements. With exoskeleton Without exoskeleton Tiled Carpet Wooden Concrete Pebbled Tiled Carpet Wooden Concrete Pebbled CRP Hip-Knee/RMS 148 ± 33 155 ± 18 158 ± 22 161 ± 27 162 ± 15 139 ± 20 313 ± 20 133 ± 30 130 ± 21 107 ± 37 Early stance 55 ± 27 53 ± 20 67 ± 30 77 ± 31 83 ± 31 82 ± 25 79 ± 22 79 ± 17 80 ± 21 52 ± 35 Midstance 6 ± 8 5 ± 5 1 ± 1 4 ± 6 2 ± 1 62 ± 21 56 ± 14 56 ± 10 58 ± 20 44 ± 20 Late stance 34 ± 7 38 ± 6 34 ± 7 35 ± 8 33 ± 7 74 ± 5 71 ± 9 73 ± 11 72 ± 8 71 ± 9 Swing CRP Knee-Ankle/RMS 82 ± 63 86 ± 59 77 ± 61 56 ± 58 50 ± 47 38 ± 47 42 ± 26 40 ± 33 28 ± 13 29 ± 14 Early stance Midstance 148 ± 50 149 ± 47 147 ± 39 141 ± 59 136 ± 57 120 ± 14 133 ± 13 125 ± 17 123 ± 15 130 ± 11 138 ± 60 129 ± 52 166 ± 13 146 ± 50 151 ± 58 87 ± 41 90 ± 20 93 ± 25 86 ± 27 112 ± 32 Late stance Swing 58 ± 30 50 ± 24 70 ± 11 71 ± 26 82 ± 28 75 ± 11 74 ± 12 74 ± 13 72 ± 28 59 ± 20 55 ± 13 57 ± 9 60 ± 11 63 ± 11 65 ± 10 75 ± 6 71 ± 7 71 ± 8 71 ± 9 63 ± 9 CRP Hip-Knee/SD 64 ± 16 64 ± 16 71 ± 5 63 ± 21 67 ± 13 89 ± 8 90 ± 8 89 ± 9 87 ± 15 84 ± 11 CRP Knee-Ankle/SD Root mean square (RMS) as the mean ± standard deviation.(0–10%) data points in one gait cycle for each participant, (10–50%) data points in one gait cycle for midstance, (50–60%) data points in one gait cycle for late stance, and (60–100%) data points in one gait cycle for the swing phase. the CRP in the early stance phase has a signifi- and in the late stance phase between the concrete pavement Hip-Knee/RMS cant difference between the tiled pavement and the concrete and the pebble pavement (paired t-tests, p =0:048). pavement (paired t-tests, p =0:02) and between the wooden With exoskeleton, there is a significant difference of the pavement and the pebble pavement (paired t-tests, p = CRP between the carpet pavement and the wooden Hip-Knee/SD 0:009). In addition, the CRP without exoskeleton pavement (paired t-tests, p =0:024) in the full gait cycle. Hip-Knee/RMS in the late stance phase has a significant difference between Without exoskeleton, there is a significant difference of the the carpet pavement and the pebble pavement (paired CRP in the full gait cycle between the tiled pave- Hip-Knee/SD t-tests, p =0:033) and between the concrete pavement ment and the concrete pavement (paired t-tests, p =0:029), and the pebble pavement (paired t-tests, p =0:033). between the tiled pavement and the pebble pavement (paired The CRP on the tiled pavement with exo- t-tests, p =0:033), between the carpet pavement and the peb- Knee-Ankle/RMS skeleton is larger than that on the other pavements in the ble pavement (paired t-tests, p =0:015), and between the early stance phase and in the midstance phase, while the wooden pavement and the pebble pavement (paired t-tests, CRP on the tiled pavement with exoskeleton is p =0:005). The trends of CRP with exoskeleton oscillate Knee-Ankle/RMS the less than that on the other pavements in the late stance more frequently than the trends of CRP without exoskeleton phase and in the swing phase. On the contrary, the over the gait cycle on the pavements. CRP on the pebble pavement with exoskeleton Knee-Ankle/RMS is the less than that on the other pavements in the early 4. Discussion stance phase and in the midstance phase, while the CRP on the tiled pavement with exoskeleton Our results suggest that the common pavements cause a sig- Knee-Ankle/RMS is larger than that on the other pavements in the late stance nificant difference of interjoint coordination with/without phase and in the swing phase. The CRP on the exoskeleton only in some phases of the gait cycle, so the Knee-Ankle/RMS pebble pavement without exoskeleton is less than that on hypothesis 1 and the hypothesis 2 are only partially proved. the other pavements in the early stance phase and in the The compressive capacity of the carpet pavement is obviously swing phase, while the CRP on the tiled pave- lower than the other pavements, which may cause the dif- Knee-Ankle/RMS ment without exoskeleton is larger than that on the other ference of CRP with exoskeleton between the Hip-Knee/RMS pavements in the midstance phase and late stance phase. carpet pavement and other pavements (except the tiled The CRP on the carpet pavement without exo- pavement) in the midstance. Moreover, the compressive Knee-Ankle/RMS skeleton is larger than that on the other pavements in the capacity of the carpet pavement may cause the difference early stance phase and in the midstance phase (as seen in of CRP with exoskeleton between the carpet Knee-Ankle/RMS Table 3). With exoskeleton, there is a significant difference pavement and the pebble pavement in the late stance of the CRP between the carpet pavement and phase and in the swing phase. However, the unevenness Knee-Ankle/RMS the pebble pavement in the late stance phase (paired t-tests, of pebble pavement as another influencing factor should p =0:027) and in the swing phase (paired t-tests, p =0:026). not be ignored. Because the unevenness of the pebble Without exoskeleton, there is a significant difference of the pavement increases the physical energy consumption CRP in the midstance phase between the tiled [18], the CRP of the pebble pavement without Knee-Ankle/RMS Hip-Knee/RMS pavement and the carpet pavement (paired t-tests, p =0:01) exoskeleton is lower than the other pavements and Applied Bionics and Biomechanics 7 statistically different from the carpet pavement and the con- ment kinematics have not been included. Second, there are crete pavement. The unevenness of the pebble pavement may not only random displacements between the human body induce the cautious dynamic neuromuscular control [13] of and the exoskeleton but also individual differences between participants and enhance their leg stiffness [1, 10] so that human bodies, which make it difficult for the human- the CRP of the pebble pavement without exoskel- exoskeleton model to measure the exact gait parameters of Hip-Knee/SD eton is smaller than that of other pavements and statistically human-exoskeleton. Therefore, in exoskeleton experiments, different from that of other pavements (except concrete there are uncertain errors in the gait parameters of human- pavement). When walking on pavements with exoskeleton, exoskeleton. Third, this study did not explore muscle adapta- participants need to adjust the center of gravity to keep the tion and joint kinetics of people who may adapt to different human-exoskeleton system balance with the help of crutches friction coefficients. Future work will focus on the effects of and prepare for the next step in stance, which may cause the different friction coefficient pavements on muscle adaptation difference of interjoint coordination patterns with exoskeleton and joint dynamics, which can further explain how people between pavements. adapt to pavements with different coefficients of friction. The exoskeleton was set in a fixed gait and joint moment, so the peak values should be similar between pavements. Data Availability However, the peak ankle dorsiflexion of walking on the car- pet pavement in the midstance is significantly different from The data that support the findings of this study are available that of walking on the pebble pavement, which may due to on request from the corresponding author, Jing Qiu. the active intervention from participants on the ankle. When the participants without exoskeleton walk on the pavements, Conflicts of Interest it is only found that the peak ankle plantar flexion in the late stance phase on the pebble pavement is significantly different The authors declare that they have no conflicts of interest. from that on the carpet pavement and the wooden pavement. This result indicates that the friction coefficients of Acknowledgments pavements do not impose on gait parameters in kinematics, but the unevenness of pavements obviously affects the gait This research was supported by the Fundamental Research parameters in kinematics [1, 10]. From the peak values with- Funds for the Central Universities of China (No. out exoskeleton at all pavements, the human mainly adjusts ZYGX2015J148). Furthermore, we are grateful for all experi- the ankle dorsiflexion in the swing phase to adapt common mental participants. pavements. Due to the fixed gait and joint moment of exoskeleton, the conditions that the knee precedes the ankle References without exoskeleton on all pavements in the early stance and in the swing phase were reversed. Similarly, the condi- [1] A. S. Voloshina, A. D. Kuo, M. A. Daley, and D. P. Ferris, tions that the hip precedes the knee without exoskeleton on “Biomechanics and energetics of walking on uneven terrain,” all pavements in the late stance phase were also reversed Journal of Experimental Biology, vol. 216, no. 21, pp. 3963– (Figure 3). 3970, 2013. [2] J.-S. Wang, C.-W. Lin, Y.-T. C. Yang, and Y.-J. Ho, “Walking pattern classification and walking distance estimation algo- 5. Conclusions and Limitations rithms using gait phase information,” IEEE Transactions on Biomedical Engineering, vol. 59, no. 10, pp. 2884–2892, 2012. In summary, our work reveals the effect of common pave- ments on interjoint coordination with/without exoskeleton. [3] T. Lenzi, M. C. Carrozza, and S. K. Agrawal, “Powered hip exo- skeletons can reduce the user’s hip and ankle muscle activa- The compressive capacity of the pavement and the uneven- tions during walking,” IEEE Transactions on Neural Systems ness of pavement are important factors that influence the and Rehabilitation Engineering, vol. 21, no. 6, pp. 938–948, interjoint coordination. The compressive capacity of the pavement can modify the magnitude of dephasing between [4] H.-J. Lee, S. Lee, W. H. Chang et al., “A wearable hip assist the hip and knee with exoskeleton in the midstance phase robot can improve gait function and cardiopulmonary meta- and in the swing phase. 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