Shapiro Mark B, Gottlieb Gerald L, Moore Charity G, Corcos Daniel M
School of Kinesiology, University of Illinois at Chicago, 60608, USA.
J Neurophysiol. 2002 Aug;88(2):1059-63. doi: 10.1152/jn.2002.88.2.1059.
This study examined the effects of unexpected loading on muscle activation during fast goal-oriented movements. We tested the hypothesis that the electromyographic (EMG) response to an unexpected load occurs at a short latency after the difference between the expected and the unexpected movement velocity exceeds a fixed threshold. Subjects performed two movement tasks as follows: 1) 30 degrees fast elbow flexion movement with an inertial load added by a torque motor; and 2) 50 degrees fast elbow flexion movement with no added load. These movement tasks were chosen to have similar timing parameters, such as movement time, time-to-peak velocity, and duration of the first agonist burst, while the magnitudes of the angular displacement, velocity, and acceleration were different. In task 1, in random trials a viscous load was substituted for the inertial load at movement onset. In task 2, the same viscous load was added in random trials. The earliest consistent response to the unexpected load was detected in the agonist (biceps) EMG at the same time, about 200 ms from the EMG onset, in both tasks. However, the velocity errors were different in the two tasks and no velocity error threshold dependency could be found. Therefore we reject the hypothesis that the timing of the EMG response to an unexpected load is related to a velocity error threshold. Instead, we suggest that the timing of the EMG response is primarily determined by descending regulation of segmental reflex gain.
本研究考察了意外负载对快速目标导向运动中肌肉激活的影响。我们测试了以下假设：当预期运动速度与意外运动速度之差超过固定阈值后，肌电图（EMG）对意外负载的反应会在短潜伏期内出现。受试者进行了如下两项运动任务：1）通过扭矩电机施加惯性负载进行30度快速屈肘运动；2）无附加负载进行50度快速屈肘运动。选择这些运动任务是为了使其具有相似的时间参数，如运动时间、达到峰值速度的时间以及首次主动肌爆发的持续时间，而角位移、速度和加速度的大小不同。在任务1中，在随机试验中，在运动开始时用粘性负载替代惯性负载。在任务2中，在随机试验中添加相同的粘性负载。在两项任务中，最早在主动肌（肱二头肌）EMG中检测到对意外负载的一致反应的时间相同，约在EMG开始后200毫秒。然而，两项任务中的速度误差不同，未发现速度误差阈值依赖性。因此，我们拒绝了EMG对意外负载的反应时间与速度误差阈值相关的假设。相反，我们认为EMG反应的时间主要由节段性反射增益的下行调节决定。
