Mathews Chase W, Clawson Delaney A, Zelik Karl E
Department of Mechanical Engineering, Vanderbilt University, Nashville, TN, United States of America.
Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States of America.
PLoS One. 2025 Jan 17;20(1):e0317259. doi: 10.1371/journal.pone.0317259. eCollection 2025.
Knee exoskeletons have been developed to assist, stabilize, or improve human movement or recovery. However, exoskeleton designers must implement transparency (i.e., get out of the way) modes during the swing phase of locomotor tasks to avoid impeding movement. The problem is that it is not understood how sensitive people are to small knee torques or what level of knee impedance is acceptable (sufficiently transparent) during swing phase. Here, we (i) characterized the biomechanical consequences of knee stiffness and damping during swing, and (ii) leveraged user perceptions of being impeded and toe clearance to define transparency thresholds, below which the participants were sufficiently unimpeded during the swing phase of gait. We conducted a series of human subject experiments that involved walking and stair ascent/descent while wearing a modified knee brace with five stiffness values ranging from 0 to 4 Nm/rad and five damping values ranging from 0 to 0.77 Nm/rad/s. We measured changes to lower limb kinematics, knee flexor muscle activity, and participants' perception of being impeded during swing. Kinematics, muscle activity, and perceived impedance all changed in response to added stiffness and damping. For stiffness, we found the median transparency thresholds for walking and stairs to be 1.76 Nm/rad and 2.95 Nm/rad, respectively, which corresponds to peak knee moments during swing of around 2.3 and 5 Nm. For damping, we found the median transparency threshold for walking and stairs to be about the same, 0.29 Nm/rad/s, which corresponds to peak knee moments during swing of around 2.3 Nm. These values provide useful benchmarks for defining quantitative design requirements for knee exoskeletons intended for locomotor activities.
膝关节外骨骼已被开发用于辅助、稳定或改善人体运动或恢复。然而，外骨骼设计者必须在运动任务的摆动阶段实施透明（即不妨碍）模式，以避免阻碍运动。问题在于，人们对小膝关节扭矩有多敏感，以及在摆动阶段何种膝关节阻抗水平是可接受的（足够透明）尚不清楚。在此，我们（i）描述了摆动过程中膝关节刚度和阻尼的生物力学后果，以及（ii）利用用户对受阻和脚趾间隙的感知来定义透明阈值，低于该阈值时参与者在步态摆动阶段受到的阻碍足够小。我们进行了一系列人体实验，让参与者佩戴经过改良的膝关节支具行走和上下楼梯，该支具具有五个刚度值，范围从0至4 Nm/rad，以及五个阻尼值，范围从0至0.77 Nm/rad/s。我们测量了下肢运动学、膝关节屈肌活动的变化，以及参与者在摆动过程中对受阻的感知。运动学、肌肉活动和感知到的阻抗均随着增加的刚度和阻尼而改变。对于刚度，我们发现行走和上楼梯时的中位透明阈值分别为1.76 Nm/rad和2.95 Nm/rad，这对应于摆动过程中膝关节峰值力矩约为2.3 Nm和5 Nm。对于阻尼，我们发现行走和上楼梯时的中位透明阈值大致相同，为0.29 Nm/rad/s，这对应于摆动过程中膝关节峰值力矩约为2.3 Nm。这些值为定义用于运动活动的膝关节外骨骼的定量设计要求提供了有用的基准。
