School of Rehabilitation Sciences, University of Ottawa, Canada.
J Biomech. 2012 Oct 11;45(15):2570-6. doi: 10.1016/j.jbiomech.2012.07.026. Epub 2012 Sep 1.
Previous investigations have identified the roles of knee joint muscles in supporting external loads during non-weight-bearing tasks and found these to depend on moment arm orientation (MAO). However, during weight-bearing tasks ground reaction forces (GRF) are transferred up through the knee, subjecting it to large multi-directional forces and stability is dependent on articular geometry, loading, and muscle activation. The purpose of this study was to investigate activation strategies used by healthy individuals to generate and support highly controlled GRF during weight-bearing. Twenty healthy males (23.9±1.9 yrs) stood with their foot in a boot fixed to a force platform. Subjects controlled an onscreen cursor by modulating normalised GRF and were required to produce 30% of their maximal force in 12 directions of the horizontal plane while maintaining 50% body weight on the test leg. Lower limb electromyography, kinematics and kinetics were recorded for each trial. Mean muscle activation was plotted in polar coordinates based on GRF orientation. Muscle activation symmetry was determined and when applicable, the mean direction of activation and muscle specificity index reported. The measured GRF were comparable to activities of daily living (0.48-0.58±0.17-0.19 N/kg in horizontal plane). Muscle activations were repeatable (ICCs: 0.78-0.98), however, only semitendinosus (ST) activation was indicated by its MAO. Considering the joint moments and activations patterns we therefore classified muscles as: (1) general joint stabilisers (vastus lateralis and medialis), (2) specific joint stabiliser (BF), and (3) moment actuators (ST and rectus femoris). General joint stabilisers were active in all load directions; specific stabilisers were active in directions opposite their MAO; moment actuators had higher specificities and activations corresponding to their MAO. We suggest the stabiliser muscles create a rigid mechanical linkage at the knee which allows the actuators of the hip and knee to modulate GRF.
先前的研究已经确定了膝关节肌肉在非负重任务中支撑外部负荷的作用，并发现这些作用取决于力臂方向（MAO）。然而，在负重任务中，地面反作用力（GRF）通过膝关节传递，使其承受多向大力量，稳定性取决于关节几何形状、负荷和肌肉激活。本研究旨在探讨健康个体在负重时产生和支撑高度受控 GRF 所使用的激活策略。20 名健康男性（23.9±1.9 岁）将脚放入固定在力台上的靴子中站立。受试者通过调节归一化 GRF 来控制屏幕上的光标，并要求在水平面上的 12 个方向产生 30%的最大力，同时保持测试腿上 50%的体重。记录每个试验的下肢肌电图、运动学和动力学。根据 GRF 方向，将平均肌肉激活绘制在极坐标中。确定肌肉激活的对称性，并在适用时报告平均激活方向和肌肉特异性指数。测量的 GRF 与日常生活活动相当（0.48-0.58±0.17-0.19 N/kg 在水平面上）。肌肉激活具有可重复性（ICC：0.78-0.98），但只有半腱肌（ST）的 MAO 指示其激活。考虑到关节力矩和激活模式，因此我们将肌肉分类为：（1）一般关节稳定器（股外侧肌和股内侧肌），（2）特定关节稳定器（BF），和（3）力矩致动器（ST 和股直肌）。一般关节稳定器在所有负载方向上均活跃；特定稳定器在与其 MAO 相反的方向上活跃；力矩致动器具有更高的特异性和与 MAO 相对应的激活。我们建议稳定器肌肉在膝关节处形成刚性机械连接，允许髋关节和膝关节的致动器调节 GRF。
