Pulse Control during Rapid Isometric Contractions of the Elbow Joint

正常受试者施加等长扭矩在快速收缩与不同幅度的目标，并在不同的速度与恒定的目标。在最快的收缩，激动剂三头肌和拮抗剂二头肌肌肉表现出一种肌电图齐射特征的慢波与初始负和随后的正相。对于不同的目标振幅，每个相位的持续时间相对恒定。在激动剂中，由负或正波形组成的面积随着目标振幅的增加而增加，并且与扭矩的一阶时间导数的峰值相关。对抗性截击与靶振幅的关系在不同的受试者中在激动剂-对抗性截击的面积和间隔上都不同。随着收缩率的降低，激动剂截击在与扭矩导数的峰值相关的区域中减少，保持恒定的持续时间，而拮抗剂截击消失。这些结果表明，快速等长收缩是由激动剂激活的调幅脉冲控制的，激动剂激活的调幅脉冲与拮抗剂激活的脉冲相关，而拮抗剂激活的脉冲在受试者中被重复利用。

Normal subjects exerted isometric torque at a rapid rate of contraction with different amplitude targets, and at different rates with a constant target. In the fastest contractions, the agonist triceps and antagonist biceps muscles showed an electromyographic volley characterized by a slow wave with an initial negative and subsequent positive phases. The duration of each phase was relatively constant for different target amplitudes. In the agonist, the area comprised by the negative or positive waveform increased with increasing target amplitude and correlated with the peak of the first time derivative of torque. The relationship of the antagonist volley to the target amplitude varied among subjects both in the area and the interval of the agonist-antagonist volley. With a decreasing contraction rate, the agonist volley decreased in the area in correlation with the peak of the torque derivative, retaining a constant duration, while the antagonist volley disappeared. These results suggest that rapid isometric contractions are controlled by an amplitude-modulated pulse of agonist activation, which is associated with a pulse of antagonist activation, while the pulse of the antagonist activation is variably utilized among subjects.