Shields R K, Law L F, Reiling B, Sass K, Wilwert J
Physical Therapy Graduate Program, College of Medicine, University of Iowa, Iowa City 52242-1008, USA.
J Appl Physiol (1985). 1997 May;82(5):1499-507. doi: 10.1152/jappl.1997.82.5.1499.
We analyzed the twitch and summated torque (tetanus) during repetitive activation and recovery of the human soleus muscle in individuals with spinal cord injury. Thirteen individuals with complete paralysis (9 chronic, 4 acute) had the tibial nerve activated every 1,500 ms with a 20-Hz train (7 stimuli) for 300 ms and a single pulse at 1,100 ms. The stimulation protocol lasted 3 min and included 120 twitches and 120 tetani. Minimal changes were found for the acute group. The chronic group showed a significant reduction in the torque and a significant slowing of the contractile speeds of both the twitch and tetanus. The decrease in the peak twitch torque was significantly greater than the decrease in the peak tetanus torque early during the fatigue protocol for the chronic group. The twitch time to peak and half relaxation time were prolonged during fatigue, which was associated with improved fusion of the tetanus torque. At the end of the fatigue protocol, the decrease in the peak twitch torque was not significantly different from the decrease in the peak tetanus torque. After 5 min of rest, the contractile speeds recovered causing the tetanus to become unfused, but the tetanus torque became less depressed than the twitch torque. The differential responses for the twitch and the tetanus suggest an interplay between optimal fusion created from contractile speed slowing and excitation contraction coupling compromise. These issues make the optimal design of functional electrical stimulation systems a formidable task.
我们分析了脊髓损伤个体在人类比目鱼肌重复激活和恢复过程中的抽搐和总和扭矩（强直收缩）。13名完全瘫痪的个体（9名慢性患者，4名急性患者），胫神经每隔1500毫秒以20赫兹的频率串（7次刺激）激活300毫秒，并在1100毫秒时给予单个脉冲。刺激方案持续3分钟，包括120次抽搐和120次强直收缩。急性组变化极小。慢性组的扭矩显著降低，抽搐和强直收缩的收缩速度显著减慢。在慢性组疲劳方案早期，抽搐峰值扭矩的下降显著大于强直收缩峰值扭矩的下降。疲劳期间，抽搐达到峰值的时间和半松弛时间延长，这与强直收缩扭矩的融合改善有关。在疲劳方案结束时，抽搐峰值扭矩的下降与强直收缩峰值扭矩的下降无显著差异。休息5分钟后，收缩速度恢复，导致强直收缩不再融合，但强直收缩扭矩的降低程度小于抽搐扭矩。抽搐和强直收缩的不同反应表明，收缩速度减慢产生的最佳融合与兴奋收缩偶联受损之间存在相互作用。这些问题使得功能性电刺激系统的优化设计成为一项艰巨的任务。
