Brown D A, Kautz S A, Dairaghi C A
VA Palo Alto Health Care System, Rehabilitation Research and Development Center, Palo Alto, CA 94304-1200, USA.
J Biomech. 1996 Oct;29(10):1349-56. doi: 10.1016/0021-9290(96)00038-3.
Gravity is a contributing force that is believed to influence strongly the control of limb movements since it affects sensory input and also contributes to task mechanics. By altering the relative contribution of gravitational force to the overall forces used to control pedaling at different body orientations, we tested the hypothesis that joint torque and muscle activation patterns would be modified to generate steady-state pedaling at altered body orientations. Eleven healthy subjects pedaled a modified ergometer at different body orientations (from horizontal to vertical), maintaining the same workload (80 J), cadence (60 rpm), and hip and knee kinematics. Pedal reaction forces and crank and pedal kinematics were measured and used to calculate joint torques and angles. EMG was recorded from four muscles (tibialis anterior, triceps surae, rectus femoris, biceps femoris). Measures of muscle activation (joint torque and EMG activity) showed strong dependence on body orientation, indicating that muscle activity is not fixed and is modified in response to altered body orientation. Simulations confirmed that, while joint torque changes were not necessary to pedal at different body orientations, observed changes were necessary to maintain consistent crank angular velocity profiles. Dependence of muscle activity on body orientation may be due to neural integration of sensory information with an internal model that includes characteristics of the endpoint, to produce consistent pedaling trajectories. Thus, both sensory consequences and mechanical aspects of gravitational forces are important determinants of locomotor tasks such as pedaling.
重力是一种起作用的力，人们认为它会强烈影响肢体运动的控制，因为它会影响感觉输入，也会对任务力学产生影响。通过改变重力对用于控制不同身体姿势下蹬踏的总力的相对贡献，我们检验了这样一个假设，即关节扭矩和肌肉激活模式会被改变，以便在改变的身体姿势下产生稳态蹬踏。11名健康受试者在不同身体姿势（从水平到垂直）下蹬踏一台改良的测力计，保持相同的工作量（80焦耳）、踏频（60转/分钟）以及髋部和膝部的运动学参数。测量踏板反作用力以及曲柄和踏板的运动学参数，并用于计算关节扭矩和角度。记录了四块肌肉（胫前肌、小腿三头肌、股直肌、股二头肌）的肌电图。肌肉激活的测量指标（关节扭矩和肌电图活动）显示出对身体姿势的强烈依赖性，表明肌肉活动不是固定不变的，而是会随着身体姿势的改变而变化。模拟结果证实，虽然在不同身体姿势下蹬踏时关节扭矩的变化并非必要，但观察到的变化对于保持一致的曲柄角速度曲线是必要的。肌肉活动对身体姿势的依赖性可能是由于感觉信息与包含端点特征的内部模型进行神经整合，从而产生一致的蹬踏轨迹。因此，重力的感觉后果和力学方面都是诸如蹬踏等运动任务的重要决定因素。
