Chang Young-Hui, Roiz Ronald A, Auyang Arick G
The Comparative Neuromechanics Laboratory, School of Applied Physiology, Georgia Institute of Technology, Atlanta, GA 30332-0356, USA.
J Biomech. 2008;41(9):1832-9. doi: 10.1016/j.jbiomech.2008.04.006. Epub 2008 May 21.
Due to the well-described spring-mass dynamics of bouncing gaits, human hopping is a tractable model for elucidating basic neuromuscular compensation principles. We tested whether subjects would employ a multi-joint or single-joint response to stabilize leg stiffness while wearing a spring-loaded ankle-foot orthosis (AFO) that applied localized resistive and assistive torques to the ankle. We analyzed kinematics and kinetics data from nine subjects hopping in place on one leg, at three frequencies (2.2, 2.4, and 2.8Hz) and three orthosis conditions (freely articulating AFO, AFO with plantarflexion resistance, and AFO with plantarflexion assistance). Leg stiffness was invariant across AFO conditions, however, compensation strategy depended upon the nature of the applied load. Biological ankle stiffness increased in response to a resistive load at twice the rate that it decreased with an assitive load. Ankle adjustments alone fully compensated for an assistive load with no net change in combined (biological plus applied) total ankle stiffness (p > or =0.133). In contrast, a resistive load resulted in a 7.4-9.0% increase in total ankle stiffness across frequencies and a concomitant 10-15% increase in knee joint stiffness at each frequency (p< or =0.037). The increased knee joint stiffness in response to resistive ankle load allowed subjects to maintain a more flexed knee at mid-stance, which attenuated the effect of the increased total ankle joint stiffness to preserve leg stiffness and whole limb biomechanical performance. Our findings suggest humans maintain invariant leg stiffness in bouncing gaits through different intralimb compensation strategies that are specific to the nature of the joint loading.
由于跳跃步态中弹簧-质量动力学已得到充分描述，人体单脚跳跃是阐明基本神经肌肉补偿原理的一个易于处理的模型。我们测试了受试者在佩戴一种对踝关节施加局部阻力和辅助扭矩的弹簧加载式踝足矫形器（AFO）时，是否会采用多关节或单关节反应来稳定腿部刚度。我们分析了九名受试者单腿原地跳跃的运动学和动力学数据，跳跃频率为三个（2.2、2.4和2.8Hz），矫形器条件为三种（自由活动的AFO、具有跖屈阻力的AFO和具有跖屈辅助的AFO）。尽管在不同AFO条件下腿部刚度不变，但补偿策略取决于所施加负荷的性质。生物性踝关节刚度对阻力负荷的增加速率是对辅助负荷减少速率的两倍。仅踝关节调整就能完全补偿辅助负荷，且组合（生物性加上所施加的）总踝关节刚度无净变化（p≥0.133）。相比之下，阻力负荷导致总踝关节刚度在各频率下增加7.4 - 9.0%，且每个频率下膝关节刚度相应增加10 - 15%（p≤0.037）。对阻力性踝关节负荷的反应中膝关节刚度增加，使受试者在支撑中期保持更弯曲的膝关节，这减弱了总踝关节刚度增加的影响，以保持腿部刚度和整个肢体的生物力学性能。我们的研究结果表明，人类在跳跃步态中通过针对关节负荷性质的不同肢体内部补偿策略来维持不变的腿部刚度。
