Department of Mechanical Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.
Hum Mov Sci. 2011 Dec;30(6):1210-24. doi: 10.1016/j.humov.2011.03.003. Epub 2011 Jun 24.
We investigated corrective reactions for backward balance losses during walking. Several biomechanical studies have suggested that backward falling can be predicted from the horizontal position and velocity of the body center of mass (COM) related to the stance foot. Our hypothesis was that corrective reactions for backward balance losses depend on whether the body moves forward or backward after a perturbation. Using a split-belt treadmill, backward balance losses during walking were induced by rapid decreases of belt speed from 3.5 km/h to 2.5, 2.0, 1.5 and 1.0 km/h. We measured kinematic data and surface electromyography (EMG) during corrective reactions while walking on the treadmill. Phase portrait analysis of COM trajectories revealed that backward balance stability was decreased by the perturbations. When the perturbed belt speed was 1.0 km/h, the COM states at toe-off were significantly lower than the stability limit; a rapid touch-down of the swing foot posterior to the stance foot then occurred, and the gait rhythm was modulated so that the phase advanced. EMG recordings during perturbed steps revealed a bilateral response, including modulation of the swing leg during the recovery. For weaker perturbations, the swing foot placements were anterior to the stance foot and there was a phase delay. In contrast to the bilateral responses for stronger perturbations, unilateral EMG responses were observed for weaker perturbations. The differences in joint kinematics and EMG patterns in the unperturbed swing leg depended on the COM states at toe-off, suggesting the existence of different responses consisting of ongoing swing movements and rapid touch-down. Thus, we conclude that corrective reactions for backward balance losses are not only phase-dependent but also state-dependent. In addition, the control system for backward balance losses predicts the feasibility of forward progression and modulates swing movement and walking rhythm according to backward balance stability.
我们研究了在行走过程中对向后平衡损失的纠正反应。几项生物力学研究表明，从身体质心（COM）的水平位置和速度相对于支撑脚，可以预测向后跌倒。我们的假设是，向后平衡损失的纠正反应取决于身体在受到干扰后是向前移动还是向后移动。使用分体式跑步机，通过快速将带速从 3.5km/h 降低到 2.5、2.0、1.5 和 1.0km/h，在行走过程中诱发向后平衡损失。当受到干扰的带速为 1.0km/h 时，COM 在离地时的状态明显低于稳定性极限；然后，摆动脚快速触地，位于支撑脚之后，步态节律被调制，相位提前。受干扰的步幅中的肌电图（EMG）记录显示出双侧反应，包括在恢复过程中摆动腿的调制。对于较弱的干扰，摆动脚的位置在支撑脚之前，存在相位延迟。与较强干扰的双侧反应相反，对于较弱的干扰，观察到单侧 EMG 反应。未受干扰的摆动腿的关节运动学和 EMG 模式的差异取决于离地时的 COM 状态，这表明存在不同的反应，包括正在进行的摆动运动和快速触地。因此，我们得出结论，向后平衡损失的纠正反应不仅取决于相位，还取决于状态。此外，向后平衡损失的控制系统预测了向前进展的可行性，并根据向后平衡稳定性调制摆动运动和行走节律。
