Comparative Neuromechanics Laboratory, School of Applied Physiology, Georgia Institute of Technology, 555 14th St NW, Atlanta, GA, 30318-0356, USA.
Exp Brain Res. 2013 Dec;231(4):433-43. doi: 10.1007/s00221-013-3708-9. Epub 2013 Oct 1.
Human walking dynamics are typically framed in the context of mechanics and energetics rather than in the context of neuromuscular control. Dynamic walking principles describe one helpful theoretical approach to characterize efficient human walking mechanics over many steps. These principles do not, however, address how such walking is controlled step-by-step despite small perturbations from natural variability. Our purpose was to identify neuromechanical control strategies used to achieve consistent and robust locomotion despite natural step-to-step force variability. We used the uncontrolled manifold concept to test whether human walkers select combinations of leading and trailing leg-forces that generate equivalent net-force trajectories during step-to-step transitions. Subjects selected leading and trailing leg-force combinations that generated consistent vertical net-force during step-to-step transitions. We conclude that vertical net-force is an implicit neuromechanical goal of human walking whose trajectory is stabilized for consistent step-to-step transitions, which agrees with the principles of dynamic walking. In contrast, inter-leg-force combinations modulated anterior-posterior net-force trajectories with each step to maintain constant walking speed, indicating that a consistent anterior-posterior net-force trajectory is not an implicit goal of walking. For a more complete picture of hierarchical locomotor control, we also tested whether each individual leg-force trajectory was stabilized through the selection of leg-force equivalent joint-torque combinations. The observed consistent vertical net-force trajectory was achieved primarily through the selection of joint-torque combinations that modulated trailing leg-force during step-to-step transitions. We conclude that humans achieve robust walking by harnessing inherent motor abundance of the joints and legs to maintain consistent step-by-step walking performance.
人类行走动力学通常是在力学和能量学的背景下进行研究，而不是在神经肌肉控制的背景下进行研究。动态行走原理描述了一种有用的理论方法，可以描述在许多步长内高效的人类行走力学。然而，这些原理并没有解决如何在受到自然变化的小干扰的情况下，一步一步地控制行走。我们的目的是确定用于实现一致和稳健运动的神经肌肉控制策略，尽管存在自然的步长力变异性。我们使用非控制流形概念来测试人类步行者是否选择了在步长过渡期间产生等效净力轨迹的前导和尾随腿力的组合。受试者选择了在步长过渡期间产生一致的垂直净力的前导和尾随腿力组合。我们得出结论，垂直净力是人类行走的一个隐含的神经肌肉目标，其轨迹在稳定的步长过渡中得到稳定，这与动态行走的原理一致。相比之下，前后净力轨迹与每一步都进行调制，以保持恒定的行走速度，这表明一致的前后净力轨迹不是行走的隐含目标。为了更全面地了解分层运动控制，我们还测试了每个单独的腿力轨迹是否通过选择腿力等效关节扭矩组合来稳定。观察到的一致的垂直净力轨迹主要是通过选择在步长过渡期间调制尾随腿力的关节扭矩组合来实现的。我们得出的结论是，人类通过利用关节和腿部固有的电机丰富性来实现稳健的行走，从而保持一致的步长行走性能。
