Moritani T, Oddson L, Thorstensson A
Department of Physiology III, Karolinska Institute, Stockholm, Sweden.
Eur J Appl Physiol Occup Physiol. 1990;60(6):425-9. doi: 10.1007/BF00705031.
Ten male subjects were tested to determine the effects of muscle fatigue upon the activation pattern of the two main ankle extensor muscles, the 'slow-twitch' soleus (SOL) and the relatively 'fast-twitch' medial gastrocnemius (MG), during a fatiguing 60-s trial of hopping to maximal height. The myoelectric signals from SOL and MG were recorded together with the vertical ground reaction force signal and analysed by means of a computer-aided electromyograph (EMG) contour analysis, i.e. two-dimensional frequency distributions were obtained relating the activation patterns of the two synergists. The EMGs were also full-wave rectified and integrated (IEMG) according to three phases of the hopping movement (PRE, pre-activation phase; ECC, eccentric phase; CON, concentric phase). Results indicated that there were significant decreases (P less than 0.01) in the peak ground reaction force, the height of hopping and the mechanical power per unit body weight at the end of the fatiguing contractions. These decreases in mechanical parameters were accompanied by significant (P less than 0.01) decreases in all three phases of MG IEMG while SOL IEMG showed no such significant declines, except in the CON phase. Thus, the decreased mechanical parameters could in large part be accounted for by the substantial and selective decline of the excitation level of the relatively fast-twitch MG muscle. Our data suggest that the centrally mediated pre-activation of the fatiguable MG muscle as well as the MG activation during the eccentric phase, which is largely controlled by supraspinal inputs and stretch-reflex modulation, are most affected by fatigue changes during repeated maximal stretch/shortening cycles of the ankle extensors.
对10名男性受试者进行了测试，以确定在60秒的疲劳单腿跳至最大高度试验中，肌肉疲劳对两块主要踝关节伸肌，即“慢肌纤维”比目鱼肌（SOL）和相对“快肌纤维”的内侧腓肠肌（MG）激活模式的影响。记录了SOL和MG的肌电信号以及垂直地面反作用力信号，并通过计算机辅助肌电图（EMG）轮廓分析进行分析，即获得了与这两块协同肌激活模式相关的二维频率分布。还根据单腿跳动作的三个阶段（PRE，预激活阶段；ECC，离心阶段；CON，向心阶段）对肌电图进行全波整流和积分（IEMG）。结果表明，在疲劳收缩结束时，峰值地面反作用力、单腿跳高度和单位体重机械功率均显著下降（P<0.01）。这些力学参数的下降伴随着MG IEMG在所有三个阶段的显著下降（P<0.01），而SOL IEMG除了在CON阶段外没有出现如此显著的下降。因此，力学参数的下降在很大程度上可以由相对快肌纤维的MG肌肉兴奋水平的实质性和选择性下降来解释。我们的数据表明，在踝关节伸肌反复进行最大拉伸/缩短循环过程中，可疲劳的MG肌肉的中枢介导预激活以及离心阶段的MG激活（这在很大程度上受脊髓上输入和牵张反射调制的控制）最容易受到疲劳变化的影响。
