Research Institute MOVE, Faculty of Human Movement Sciences, VU University Amsterdam, Van der Boechorststraat 9, NL-1081 BT Amsterdam, the Netherlands.
J Biomech. 2011 Jan 4;44(1):121-7. doi: 10.1016/j.jbiomech.2010.08.036.
External perturbations during pushing tasks have been suggested to be a risk factor for low-back symptoms. An experiment was designed to investigate whether self-induced and externally induced sudden stops while pushing a high inertia cart influence trunk motions, and how flexor and extensor muscles counteract these perturbations. Twelve healthy male participants pushed a 200 kg cart at shoulder height and hip height. Pushing while walking was compared to situations in which participants had to stop the cart suddenly (self-induced stop) or in which the wheels of the cart were unexpectedly blocked (externally induced stop). For the perturbed conditions, the peak values and the maximum changes from the reference condition (pushing while walking) of the external moment at L5/S1, trunk inclination and electromyographic amplitudes of trunk muscles were determined. In the self-induced stop, a voluntary trunk extension occurred. Initial responses in both stops consisted of flexor and extensor muscle cocontraction. In self-induced stops this was followed by sustained extensor activity. In the externally induced stops, an external extension moment caused a decrease in trunk inclination. The opposite directions of the internal moment and trunk motion in the externally induced stop while pushing at shoulder height may indicate insufficient active control of trunk posture. Consequently, sudden blocking of the wheels in pushing at shoulder height may put the low back at risk of mechanical injury.
外界干扰在推动任务中被认为是导致下背部症状的一个危险因素。一项实验旨在研究推动高惯性手推车时，自我诱导和外部诱导的突然停止是否会影响躯干运动，以及屈肌和伸肌如何抵消这些干扰。12 名健康男性参与者以肩高和髋高推动一辆 200 公斤的手推车。与推动行走时相比，参与者需要突然停止推车（自我诱导停止）或推车的轮子意外受阻（外部诱导停止）的情况。对于受干扰的情况，确定 L5/S1 处外部力矩、躯干倾斜和躯干肌肉肌电图幅度的峰值值以及相对于参考条件（推动行走）的最大变化。在自我诱导停止中，发生了自愿的躯干伸展。在两种停止情况下的初始反应都是屈肌和伸肌协同收缩。在自我诱导停止中，随后是持续的伸肌活动。在外力诱导停止时，外部伸展力矩会导致躯干倾斜度减小。在肩高推动时外部停止时内部力矩和躯干运动的相反方向可能表明对躯干姿势的主动控制不足。因此，在肩高推动时突然阻止车轮可能会使腰部容易受到机械损伤。
