Selgrade Brian P, Toney Megan E, Chang Young-Hui
Comparative Neuromechanics Laboratory School of Applied Physiology, Georgia Institute of Technology, Atlanta, GA, USA.
Comparative Neuromechanics Laboratory School of Applied Physiology, Georgia Institute of Technology, Atlanta, GA, USA.
J Biomech. 2017 Feb 28;53:136-143. doi: 10.1016/j.jbiomech.2017.01.012. Epub 2017 Jan 14.
Locomotor adaptation is commonly studied using split-belt treadmill walking, in which each foot is placed on a belt moving at a different speed. As subjects adapt to split-belt walking, they reduce metabolic power, but the biomechanical mechanism behind this improved efficiency is unknown. Analyzing mechanical work performed by the legs and joints during split-belt adaptation could reveal this mechanism. Because ankle work in the step-to-step transition is more efficient than hip work, we hypothesized that control subjects would reduce hip work on the fast belt and increase ankle work during the step-to-step transition as they adapted. We further hypothesized that subjects with unilateral, trans-tibial amputation would instead increase propulsive work from their intact leg on the slow belt. Control subjects reduced hip work and shifted more ankle work to the step-to-step transition, supporting our hypothesis. Contrary to our second hypothesis, intact leg work, ankle work and hip work in amputees were unchanged during adaptation. Furthermore, all subjects increased collisional energy loss on the fast belt, but did not increase propulsive work. This was possible because subjects moved further backward during fast leg single support in late adaptation than in early adaptation, compensating by reducing backward movement in slow leg single support. In summary, subjects used two strategies to improve mechanical efficiency in split-belt walking adaptation: a CoM displacement strategy that allows for less forward propulsion on the fast belt; and, an ankle timing strategy that allows efficient ankle work in the step-to-step transition to increase while reducing inefficient hip work.
运动适应通常采用分带跑步机行走来进行研究，即每只脚放置在以不同速度移动的皮带上。当受试者适应分带行走时，他们会降低代谢功率，但这种效率提高背后的生物力学机制尚不清楚。分析分带适应过程中腿部和关节所做的机械功可能会揭示这一机制。由于在步间转换时踝关节的功比髋关节的功更有效，我们假设对照组受试者在适应过程中会减少在快速皮带上的髋关节功，并增加步间转换时的踝关节功。我们还假设，单侧经胫截肢的受试者反而会增加其健全腿在慢速皮带上的推进功。对照组受试者减少了髋关节功，并将更多的踝关节功转移到步间转换，支持了我们的假设。与我们的第二个假设相反，截肢者的健全腿功、踝关节功和髋关节功在适应过程中没有变化。此外，所有受试者在快速皮带上的碰撞能量损失都增加了，但推进功没有增加。这是可能的，因为在适应后期，受试者在快速腿单支撑期间比早期向后移动得更远，通过减少慢速腿单支撑期间的向后移动来进行补偿。总之，受试者在分带行走适应中采用了两种策略来提高机械效率：一种是质心位移策略，即在快速皮带上减少向前推进；另一种是踝关节定时策略，即允许在步间转换时高效的踝关节功增加，同时减少低效的髋关节功。
