Stanford University, Department of Mechanical Engineering, Stanford, CA 94305, USA.
Stanford University, Department of Bioengineering, Stanford, CA 94305, USA.
J Exp Biol. 2019 Sep 3;222(Pt 17):jeb202895. doi: 10.1242/jeb.202895.
Human running is inefficient. For every 10 calories burned, less than 1 is needed to maintain a constant forward velocity - the remaining energy is, in a sense, wasted. The majority of this wasted energy is expended to support the bodyweight and redirect the center of mass during the stance phase of gait. An order of magnitude less energy is expended to brake and accelerate the swinging leg. Accordingly, most devices designed to increase running efficiency have targeted the costlier stance phase of gait. An alternative approach is seen in nature: spring-like tissues in some animals and humans are believed to assist leg swing. While it has been assumed that such a spring simply offloads the muscles that swing the legs, thus saving energy, this mechanism has not been experimentally investigated. Here, we show that a spring, or 'exotendon', connecting the legs of a human reduces the energy required for running by 6.4±2.8%, and does so through a complex mechanism that produces savings beyond those associated with leg swing. The exotendon applies assistive forces to the swinging legs, increasing the energy optimal stride frequency. Runners then adopt this frequency, taking faster and shorter strides, and reduce the joint mechanical work to redirect their center of mass. Our study shows how a simple spring improves running economy through a complex interaction between the changing dynamics of the body and the adaptive strategies of the runner, highlighting the importance of considering each when designing systems that couple human and machine.
人类跑步效率低下。每消耗 10 卡路里，只有不到 1 卡路里用于维持恒定的前进速度——其余的能量在某种意义上被浪费了。大部分浪费的能量用于支撑体重，并在步态的支撑阶段重新引导质心。只有更小的一部分能量用于制动和加速摆动腿。因此，大多数旨在提高跑步效率的设备都针对步态更昂贵的支撑阶段。一种替代方法可以在自然界中看到：一些动物和人类的弹簧状组织被认为有助于腿部摆动。虽然人们认为这样的弹簧只是减轻了摆动腿部的肌肉的负担，从而节省了能量，但这种机制尚未经过实验研究。在这里，我们表明连接人体腿部的弹簧或“外肌腱”可以将跑步所需的能量降低 6.4±2.8%，并且通过一种复杂的机制来实现节省，这种机制产生的节省超出了与腿部摆动相关的节省。外肌腱对摆动的腿部施加辅助力，增加了能量最优的步频。跑步者然后采用这种频率，迈出更快、更短的步伐，并减少重新引导质心的关节机械功。我们的研究表明，一个简单的弹簧如何通过身体动态的复杂相互作用以及跑步者的自适应策略来提高跑步经济性，这突出了在设计将人和机器结合起来的系统时，考虑到这两者的重要性。
