Galle Samuel, Malcolm Philippe, Collins Steven Hartley, De Clercq Dirk
Department of Movement and Sports Sciences, Ghent University, Watersportlaan 2, 9000, Gent, Belgium.
Department of Biomechanics and Center for Research in Human Movement Variability, University of Nebraska at Omaha, 6160 University Dr S, Omaha, NE, 68182, USA.
J Neuroeng Rehabil. 2017 Apr 27;14(1):35. doi: 10.1186/s12984-017-0235-0.
Powered ankle-foot exoskeletons can reduce the metabolic cost of human walking to below normal levels, but optimal assistance properties remain unclear. The purpose of this study was to test the effects of different assistance timing and power characteristics in an experiment with a tethered ankle-foot exoskeleton.
Ten healthy female subjects walked on a treadmill with bilateral ankle-foot exoskeletons in 10 different assistance conditions. Artificial pneumatic muscles assisted plantarflexion during ankle push-off using one of four actuation onset timings (36, 42, 48 and 54% of the stride) and three power levels (average positive exoskeleton power over a stride, summed for both legs, of 0.2, 0.4 and 0.5 W∙kg). We compared metabolic rate, kinematics and electromyography (EMG) between conditions.
Optimal assistance was achieved with an onset of 42% stride and average power of 0.4 W∙kg, leading to 21% reduction in metabolic cost compared to walking with the exoskeleton deactivated and 12% reduction compared to normal walking without the exoskeleton. With suboptimal timing or power, the exoskeleton still reduced metabolic cost, but substantially less so. The relationship between timing, power and metabolic rate was well-characterized by a two-dimensional quadratic function. The assistive mechanisms leading to these improvements included reducing muscular activity in the ankle plantarflexors and assisting leg swing initiation.
These results emphasize the importance of optimizing exoskeleton actuation properties when assisting or augmenting human locomotion. Our optimal assistance onset timing and average power levels could be used for other exoskeletons to improve assistance and resulting benefits.
动力踝足外骨骼可将人类行走的代谢成本降低至正常水平以下，但最佳辅助特性仍不明确。本研究的目的是在一项使用系留式踝足外骨骼的实验中测试不同辅助时机和功率特性的影响。
10名健康女性受试者在跑步机上佩戴双侧踝足外骨骼，处于10种不同的辅助条件下行走。人工气动肌肉在踝关节蹬离阶段辅助跖屈，采用四种驱动起始时机之一（步幅的36%、42%、48%和54%）和三种功率水平（双腿步幅上平均正外骨骼功率，总和为0.2、0.4和0.5W∙kg）。我们比较了不同条件下的代谢率、运动学和肌电图（EMG）。
在步幅42%的起始时机和平均功率0.4W∙kg时实现了最佳辅助，与外骨骼停用状态下行走相比，代谢成本降低了21%，与无外骨骼的正常行走相比降低了12%。在时机或功率不理想时，外骨骼仍能降低代谢成本，但降低幅度明显较小。时机、功率和代谢率之间的关系可用二维二次函数很好地描述。导致这些改善的辅助机制包括减少踝关节跖屈肌的肌肉活动和辅助腿部摆动起始。
这些结果强调了在辅助或增强人类运动时优化外骨骼驱动特性的重要性。我们的最佳辅助起始时机和平均功率水平可用于其他外骨骼，以改善辅助效果和带来的益处。
