School of Applied Physiology, Georgia Institute of Technology, Atlanta, Georgia, USA.
PLoS One. 2013 Jul 30;8(7):e69429. doi: 10.1371/journal.pone.0069429. Print 2013.
Humans can robustly locomote over complex terrains even while simultaneously attending to other tasks such as accurate foot placement on the ground. We investigated whether subjects would exploit motor redundancy across the joints of the leg to stabilize overall limb kinematics when presented with a hopping task that constrained foot placement position. Subjects hopped in place on one leg (2.2 Hz) while having to place their foot into one of three target sizes upon landing (0.250, 0.063, 0.010 m(2)). As takeoff and landing angles are critical to this task performance, we hypothesized smaller target sizes would increase the need to stabilize (i.e., make more consistent) the leg orientation through motor equivalent combinations of segment angles. As it was not critical to the targeting task, we hypothesized no changes for leg length stabilization across target size. With smaller target sizes, we saw total segment angle variance increase due to greater signal-dependent noise associated with an increased activation of leg extensor muscles (medial and lateral gastrocnemius, vastus medialis, vastus lateralis and rectus femoris). At smaller target sizes, more segment angle variance was aligned to kinematic deviations with the goal of maintaining leg orientation trajectory. We also observed a decrease in the variance structure for stabilizing leg length at the smallest target conditions. This trade-off effect is explained by the nearly orthogonal relationship between the two goal-equivalent manifolds for leg length vs. leg orientation stabilization. Our results suggest humans increasingly rely on kinematic redundancy in their legs to achieve robust, consistent locomotion when faced with novel conditions that constrain performance requirements. These principles may generalize to other human locomotor gaits and provide important insights into the control of the legs during human walking and running.
人类即使在同时进行其他任务（例如准确地将脚放在地面上）时，也能在复杂的地形上稳健地移动。我们研究了当呈现出限制脚放置位置的跳跃任务时，受试者是否会利用腿部关节的运动冗余来稳定整体肢体运动学。受试者以单腿（2.2Hz）原地跳跃，同时在落地时将脚放入三个目标尺寸中的一个（0.250、0.063、0.010m²）。由于起飞和着陆角度对任务表现至关重要，我们假设较小的目标尺寸会增加通过运动等效的角度组合来稳定（即更一致）腿部方向的需求。由于对目标任务不重要，我们假设在目标尺寸不变的情况下，腿部长度稳定性不会改变。对于较小的目标尺寸，我们看到总节段角度方差增加，这是由于与腿部伸肌（内侧和外侧腓肠肌、股直肌、股外侧肌和股内侧肌）的激活增加相关的更大的信号依赖噪声。在较小的目标尺寸下，更多的节段角度方差与运动学偏差对齐，以保持腿部方向轨迹。我们还观察到在最小目标条件下稳定腿部长度的方差结构减少。这种权衡效应是由腿部长度与腿部方向稳定的两个目标等效流形之间的几乎正交关系解释的。我们的结果表明，当面临限制性能要求的新条件时，人类会越来越依赖腿部的运动冗余来实现稳健、一致的运动。这些原则可能适用于其他人类运动步态，并为人类行走和跑步时腿部的控制提供重要的见解。
