Joint Department of Biomedical Engineering, UNC Chapel Hill and NC State University, Raleigh, NC, 27607, USA.
John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA.
Sci Rep. 2020 Feb 27;10(1):3604. doi: 10.1038/s41598-020-60360-4.
Unpowered exoskeletons with springs in parallel to human plantar flexor muscle-tendons can reduce the metabolic cost of walking. We used ultrasound imaging to look 'under the skin' and measure how exoskeleton stiffness alters soleus muscle contractile dynamics and shapes the user's metabolic rate during walking. Eleven participants (4F, 7M; age: 27.7 ± 3.3 years) walked on a treadmill at 1.25 m s and 0% grade with elastic ankle exoskeletons (rotational stiffness: 0-250 Nm rad) in one training and two testing days. Metabolic savings were maximized (4.2%) at a stiffness of 50 Nm rad. As exoskeleton stiffness increased, the soleus muscle operated at longer lengths and improved economy (force/activation) during early stance, but this benefit was offset by faster shortening velocity and poorer economy in late stance. Changes in soleus activation rate correlated with changes in users' metabolic rate (p = 0.038, R = 0.44), highlighting a crucial link between muscle neuromechanics and exoskeleton performance; perhaps informing future 'muscle-in-the loop' exoskeleton controllers designed to steer contractile dynamics toward more economical force production.
无动力的外骨骼与人类足底屈肌肌腱平行的弹簧可以降低步行的代谢成本。我们使用超声成像来“透视皮肤”，测量外骨骼刚度如何改变比目鱼肌的收缩动力学，并在步行过程中塑造用户的代谢率。11 名参与者（4 名女性，7 名男性；年龄：27.7±3.3 岁）在跑步机上以 1.25m/s 和 0%坡度行走，穿着弹性踝关节外骨骼（旋转刚度：0-250Nm rad），在一个训练日和两个测试日进行。在刚度为 50Nm rad 时，代谢节省达到最大值（4.2%）。随着外骨骼刚度的增加，比目鱼肌在早期站立时以更长的长度和更高的经济性（力/激活）工作，但这种益处被后期站立时更快的缩短速度和更低的经济性所抵消。比目鱼肌激活率的变化与使用者代谢率的变化相关（p=0.038，R=0.44），这突出了肌肉神经力学和外骨骼性能之间的关键联系；也许为未来旨在引导收缩动力学向更经济的力产生的“肌肉在回路”外骨骼控制器提供了信息。
