Robust passive dynamics of the musculoskeletal system compensate for unexpected surface changes during human hopping.
Robust passive dynamics of the musculoskeletal system compensate for unexpected surface changes during human hopping.
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DOI：
10.1152/japplphysiol.91189.2008
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发表时间：
2009-09
影响因子：
3.3
通讯作者：
M. M. van der Krogt-M.;W. D. de Graaf;C. T. Farley;C. Moritz;L. J. Richard Casius;M. Bobbert
中科院分区：
文献类型：
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作者：
M. M. van der Krogt-M.;W. D. de Graaf;C. T. Farley;C. Moritz;L. J. Richard Casius;M. Bobbert
当人类跳跃者对表面硬度的变化感到惊讶时，他们几乎立即通过改变腿部硬度来适应，这意味着神经反馈不是必要的。这项模拟研究的目的首先是研究当着陆在意想不到的硬表面或意想不到的柔顺(软)表面时，腿部僵硬是否可以在没有神经控制调整的情况下发生变化，其次确定导致腿部僵硬变化的潜在机制。对前向动态肌肉骨骼模型的肌肉刺激模式进行了优化，使其与硬面和软面上的实验跳跃运动学相匹配。接下来，只改变表面刚度，以确定肌肉骨骼模型与意外表面的机械相互作用如何影响腿部刚度。研究发现，腿的僵硬被动地适应了这两种意想不到的表面。在意想不到的硬面上，腿部的刚度低于软面上的，导致接近正常的质心位移。腿部僵硬的减少是由于较低的有效肌肉僵硬导致的关节僵硬的结果。由于与坚硬表面的相互作用，关节的更快弯曲导致肌肉长度的更大变化，而规定的活动状态和由此产生的肌力的增加在时间上几乎保持不变。在意想不到的软表面上发现了相反的效应，表明了被动动力学的双向稳定特性。这些对意外表面的被动适应在跨越不同地形的移动过程中协调干扰时可能是至关重要的。
When human hoppers are surprised by a change in surface stiffness, they adapt almost instantly by changing leg stiffness, implying that neural feedback is not necessary. The goal of this simulation study was first to investigate whether leg stiffness can change without neural control adjustment when landing on an unexpected hard or unexpected compliant (soft) surface, and second to determine what underlying mechanisms are responsible for this change in leg stiffness. The muscle stimulation pattern of a forward dynamic musculoskeletal model was optimized to make the model match experimental hopping kinematics on hard and soft surfaces. Next, only surface stiffness was changed to determine how the mechanical interaction of the musculoskeletal model with the unexpected surface affected leg stiffness. It was found that leg stiffness adapted passively to both unexpected surfaces. On the unexpected hard surface, leg stiffness was lower than on the soft surface, resulting in close-to-normal center of mass displacement. This reduction in leg stiffness was a result of reduced joint stiffness caused by lower effective muscle stiffness. Faster flexion of the joints due to the interaction with the hard surface led to larger changes in muscle length, while the prescribed increase in active state and resulting muscle force remained nearly constant in time. Opposite effects were found on the unexpected soft surface, demonstrating the bidirectional stabilizing properties of passive dynamics. These passive adaptations to unexpected surfaces may be critical when negotiating disturbances during locomotion across variable terrain.