Nuckols Richard W, Takahashi Kota Z, Farris Dominic J, Mizrachi Sarai, Riemer Raziel, Sawicki Gregory S
School of Engineering and Applied Sciences, Harvard University and Wyss Institute, Cambridge, Massachusetts, United States of America.
Department of Biomechanics, University of Nebraska at Omaha, Omaha, Nebraska, United States of America.
PLoS One. 2020 Aug 28;15(8):e0231996. doi: 10.1371/journal.pone.0231996. eCollection 2020.
Lower-limb wearable robotic devices can improve clinical gait and reduce energetic demand in healthy populations. To help enable real-world use, we sought to examine how assistance should be applied in variable gait conditions and suggest an approach derived from knowledge of human locomotion mechanics to establish a 'roadmap' for wearable robot design. We characterized the changes in joint mechanics during walking and running across a range of incline/decline grades and then provide an analysis that informs the development of lower-limb exoskeletons capable of operating across a range of mechanical demands. We hypothesized that the distribution of limb-joint positive mechanical power would shift to the hip for incline walking and running and that the distribution of limb-joint negative mechanical power would shift to the knee for decline walking and running. Eight subjects (6M,2F) completed five walking (1.25 m s-1) trials at -8.53°, -5.71°, 0°, 5.71°, and 8.53° grade and five running (2.25 m s-1) trials at -5.71°, -2.86°, 0°, 2.86°, and 5.71° grade on a treadmill. We calculated time-varying joint moment and power output for the ankle, knee, and hip. For each gait, we examined how individual limb-joints contributed to total limb positive, negative and net power across grades. For both walking and running, changes in grade caused a redistribution of joint mechanical power generation and absorption. From level to incline walking, the ankle's contribution to limb positive power decreased from 44% on the level to 28% at 8.53° uphill grade (p < 0.0001) while the hip's contribution increased from 27% to 52% (p < 0.0001). In running, regardless of the surface gradient, the ankle was consistently the dominant source of lower-limb positive mechanical power (47-55%). In the context of our results, we outline three distinct use-modes that could be emphasized in future lower-limb exoskeleton designs 1) Energy injection: adding positive work into the gait cycle, 2) Energy extraction: removing negative work from the gait cycle, and 3) Energy transfer: extracting energy in one gait phase and then injecting it in another phase (i.e., regenerative braking).
下肢可穿戴机器人设备能够改善临床步态并降低健康人群的能量需求。为了有助于实现其在现实世界中的应用，我们试图研究在不同步态条件下应如何提供辅助，并提出一种源自人类运动力学知识的方法，以建立可穿戴机器人设计的“路线图”。我们对在一系列上坡/下坡坡度下行走和跑步过程中的关节力学变化进行了表征，然后提供了一项分析，为能够在一系列机械需求下运行的下肢外骨骼的开发提供参考。我们假设，在上坡行走和跑步时，肢体关节正机械功率的分布会向髋部转移，而在下坡行走和跑步时，肢体关节负机械功率的分布会向膝部转移。八名受试者（6名男性，2名女性）在跑步机上完成了五项行走（速度为1.25米/秒）试验，坡度分别为-8.53°、-5.71°、0°、5.71°和8.53°，以及五项跑步（速度为2.25米/秒）试验，坡度分别为-5.71°、-2.86°、0°、2.86°和5.71°。我们计算了踝关节、膝关节和髋关节随时间变化的关节力矩和功率输出。对于每种步态，我们研究了各个肢体关节在不同坡度下对肢体总正功率、负功率和净功率的贡献。对于行走和跑步，坡度的变化都会导致关节机械功率产生和吸收的重新分布。从平路到上坡行走时，踝关节对肢体正功率的贡献从平路时的44%下降到8.53°上坡坡度时的28%（p<0.0001），而髋部的贡献则从27%增加到52%（p<0.0001）。在跑步时，无论表面坡度如何，踝关节始终是下肢正机械功率的主要来源（47%-55%）。基于我们的研究结果，我们概述了未来下肢外骨骼设计中可以强调的三种不同使用模式：1）能量注入：在步态周期中增加正功；2）能量提取：从步态周期中去除负功；3）能量转移：在一个步态阶段提取能量，然后在另一个阶段注入能量（即再生制动）。
