Rüegg D G, Bongioanni F
Institute of Physiology, University of Fribourg, Switzerland.
Exp Brain Res. 1989;77(2):412-20. doi: 10.1007/BF00274999.
In a visual reaction time task, human subjects superimposed isometric ballistic contractions on a maintained activity in the soleus or anterior tibial muscle. Since there were good reasons to believe that the supraspinal motor commands for the ballistic contractions were independent of those for the background activity, the interaction between the motor commands for the ballistic and for the steady contractions could be studied at the spinal level. If ballistic and steady contractions were in the same direction, the EMG burst and torque changes associated with the ballistic contraction were nearly constant irrespective of the maintained steady flexion force. This was true if a muscle was activated to about 5% of its maximum force as the soleus muscle during plantar flexions and if it was activated to about 40% of its maximum force as the anterior tibial muscle during dorsal flexions. If ballistic and steady contractions were in opposite directions the torque changes related to the ballistic contraction increased linearly with the background activity. This relation was caused by a reduction in antagonist activity starting about 50 ms before the agonist EMG burst and not by an increased agonist burst, the latter remaining independent of background activity. These results imply that the input-output relationship of the motoneuronal pool is nearly linear. The functional basis of this relation is the size principle which is valid during continuous and ballistic contractions. The number of motor units recruited for the ballistic contraction is adjusted according to their force such that the contraction amplitude remains constant.
在一项视觉反应时间任务中，人类受试者在比目鱼肌或胫骨前肌的持续活动上叠加等长弹道收缩。由于有充分理由相信弹道收缩的脊髓上运动指令与背景活动的指令相互独立，因此可以在脊髓水平研究弹道收缩和稳定收缩的运动指令之间的相互作用。如果弹道收缩和稳定收缩方向相同，与弹道收缩相关的肌电图爆发和扭矩变化几乎恒定，而与维持的稳定屈曲力无关。当肌肉在跖屈时像比目鱼肌一样被激活到其最大力的约5%，以及在背屈时像胫骨前肌一样被激活到其最大力的约40%时，情况就是如此。如果弹道收缩和稳定收缩方向相反，与弹道收缩相关的扭矩变化会随着背景活动呈线性增加。这种关系是由在激动剂肌电图爆发前约50毫秒开始的拮抗剂活动减少引起的，而不是由激动剂爆发增加引起的，后者保持与背景活动无关。这些结果意味着运动神经元池的输入-输出关系几乎是线性的。这种关系的功能基础是大小原则，该原则在持续和弹道收缩期间均有效。为弹道收缩募集的运动单位数量会根据其力量进行调整，以使收缩幅度保持恒定。
