Research Institute MOVE, Faculty of Human Movement Sciences, VU University Amsterdam, Van der Boechorststraat 9, NL-1081 BT Amsterdam, the Netherlands.
J Biomech. 2010 May 7;43(7):1364-72. doi: 10.1016/j.jbiomech.2010.01.022. Epub 2010 Feb 18.
Cyclic activation of the external and internal oblique muscles contributes to twisting moments during normal gait. During pushing while walking, it is not well understood how these muscles respond to presence of predictable (cyclic push-off forces) and unpredictable (external) perturbations that occur in pushing tasks. We hypothesized that the predictable perturbations due to the cyclic push-off forces would be associated with cyclic muscle activity, while external perturbations would be counteracted by cocontraction of the oblique abdominal muscles. Eight healthy male subjects pushed at two target forces and two handle heights in a static condition and while walking without and with external perturbations. For all pushing tasks, the median, the static (10th percentile) and the peak levels (90th percentile) of the electromyographic amplitudes were determined. Linear models with oblique abdominal EMGs and trunk angles as input were fit to the twisting moments, to estimate trunk stiffness. There was no significant difference between the static EMG levels in pushing while walking compared to the peak levels in pushing while standing. When pushing while walking, the additional dynamic activity was associated with the twisting moments, which were actively modulated by the pairs of oblique muscles as in normal gait. The median and static levels of trunk muscle activity and estimated trunk stiffness were significantly higher when perturbations occurred than without perturbations. The increase baseline of muscle activity indicated cocontraction of the antagonistic muscle pairs. Furthermore, this cocontraction resulted in an increased trunk stiffness around the longitudinal axis.
在正常步态中，外斜肌和内斜肌的循环激活有助于产生扭转力矩。在行走时推物时，人们对外斜肌在推物任务中对可预测（周期性推离力）和不可预测（外部）干扰的反应方式了解甚少。我们假设，由于周期性推离力而产生的可预测干扰会与周期性肌肉活动相关，而外部干扰会通过腹斜肌的共收缩来抵消。8 名健康男性在静态和行走时（有无外部干扰）以两种目标力和两种手柄高度进行推物。对于所有推物任务，均确定肌电图幅度的中位数、静态（第 10 百分位数）和峰值（第 90 百分位数）水平。使用腹斜肌肌电图和躯干角度作为输入的线性模型拟合扭转力矩，以估计躯干刚度。与站立时推物的峰值水平相比，行走时推物的静态肌电图水平没有显著差异。当行走时推物时，额外的动态活动与扭转力矩相关，就像在正常步态中一样，这些扭转力矩由对侧斜肌主动调节。与没有干扰时相比，发生干扰时躯干肌肉活动的中位数和静态水平以及估计的躯干刚度显著更高。肌肉活动基线增加表明拮抗肌对的共收缩。此外，这种共收缩导致围绕纵轴的躯干刚度增加。
