Löscher W N, Cresswell A G, Thorstensson A
Department of Neurology, Landesnervenklinik, Salzburg, Austria.
Acta Physiol Scand. 1994 Sep;152(1):73-82. doi: 10.1111/j.1748-1716.1994.tb09786.x.
The objective was to investigate electromyographic activity (EMG) and isometric force tremor (IFT) changes during a sustained sub-maximal isometric contraction in two muscles acting upon the same joint but differing in muscle fibre composition. Surface and intra-muscular EMG activity from the gastrocnemius and soleus muscles and IFT were recorded during an exhausting isometric plantar flexion (30% of maximal voluntary contraction). Surface EMG amplitude (RMS) of both gastrocnemius and soleus muscles increased significantly over time. Gastrocnemius EMG RMS increased in a non-linear fashion while soleus EMG RMS increased linearly. A significant linear decrease of surface EMG mean power frequency (MPF) was observed over time for both muscles. The decrease in gastrocnemius MPF was significantly greater than that for soleus. Intra-muscular EMG results showed similar trends. Correlations of intramuscular EMG RMS and MPF with time were, however, characterized by lower correlation coefficients than those from the surface EMG. Isometric force tremor RMS significantly increased non-linearly with duration of contraction, while IFT MPF showed a significant linear decrease with time. Changes in surface EMG RMS were correlated to changes seen in IFT RMS, in particular, for the predominantly fast twitch gastrocnemius muscle. Correlation coefficients of surface EMG MPF and IFT MPF were lower than RMS correlations. The associated changes in IFT and EMG with fatigue indicate alterations in motor unit firing rate, recruitment and synchronization. The muscle specificity of the EMG and IFT changes suggests a coupling to muscle fibre type composition, although differences in the relative force contribution of each muscle could also affect the results.
目的是研究在作用于同一关节但肌纤维组成不同的两块肌肉进行持续次最大等长收缩期间的肌电图活动（EMG）和等长力量震颤（IFT）变化。在进行疲劳性等长跖屈（最大自主收缩的30%）期间，记录腓肠肌和比目鱼肌的表面肌电图和肌内肌电图活动以及IFT。随着时间的推移，腓肠肌和比目鱼肌的表面肌电图振幅（均方根值）均显著增加。腓肠肌肌电图均方根值呈非线性增加，而比目鱼肌肌电图均方根值呈线性增加。随着时间的推移，观察到两块肌肉的表面肌电图平均功率频率（MPF）均显著线性下降。腓肠肌MPF的下降显著大于比目鱼肌。肌内肌电图结果显示出类似趋势。然而，肌内肌电图均方根值和MPF与时间的相关性的相关系数低于表面肌电图的相关系数。等长力量震颤均方根值随收缩持续时间显著非线性增加，而IFT MPF随时间呈显著线性下降。表面肌电图均方根值的变化与IFT均方根值的变化相关，特别是对于主要为快肌纤维的腓肠肌。表面肌电图MPF和IFT MPF的相关系数低于均方根值的相关性。IFT和肌电图随疲劳的相关变化表明运动单位放电频率、募集和同步性发生了改变。肌电图和IFT变化的肌肉特异性表明与肌纤维类型组成有关，尽管每块肌肉相对力量贡献的差异也可能影响结果。
