Crenshaw A G, Karlsson S, Gerdle B, Fridén J
Department of Physiology and Technology, National Institute for Working Life, Umeå, Sweden.
Acta Physiol Scand. 1997 Aug;160(4):353-61. doi: 10.1046/j.1365-201X.1997.00168.x.
This study investigated changes in intramuscular pressure (IMP) and surface electromyographic (EMG) parameters (mean frequency of the power spectrum, f(mean); and signal amplitude denoted as root mean square, RMS) during contractions to fatigue at 25 and 70% of maximal voluntary contraction (MVC). Parameters were recorded simultaneously from the vastus lateralis muscle during knee extension. A significant decrease in f(mean) occurred with time at both contraction levels; however, the rate of decline (slope) was greater at 70% MVC. RMS increased throughout the contractions at both levels, with the relative increase being significantly greater for 25% MVC. IMP increased during 25% MVC but did not change during the 70% MVC contraction. IMP at rest was significantly higher post-contractions than it was pre-contractions at 25% MVC (21.1 vs. 8.0 mmHg, P < 0.01) and 70% MVC (13.7 vs. 8.6 mmHg, P < 0.01). Consequently, post-contraction IMP was higher at 25% MVC than at 70% MVC (P < 0.01). IMP changes throughout the fatiguing contractions correlated negatively with f(mean) and positively with RMS at both MVC levels; however, these correlations were better at 25% MVC. The extent of intramuscular water accumulation is discussed as a major cause of the difference in IMP changes between 25% and 70% MVC. Significant differences in the rate of change for all parameters between high vs. low contraction levels may suggest a common mechanism governing changes in IMP and EMG fatigue indicators.
本研究调查了在最大自主收缩（MVC）的25%和70%强度下进行收缩至疲劳过程中，肌肉内压力（IMP）和表面肌电图（EMG）参数（功率谱的平均频率，f(mean)；以及表示为均方根的信号幅度，RMS）的变化。在膝关节伸展过程中，同时从股外侧肌记录这些参数。在两个收缩水平下，f(mean)均随时间显著下降；然而，在70%MVC时下降速率（斜率）更大。在两个水平的收缩过程中，RMS均增加，且25%MVC时的相对增加幅度显著更大。在25%MVC收缩过程中IMP增加，但在70%MVC收缩过程中未改变。在25%MVC和70%MVC时，收缩后休息时的IMP显著高于收缩前（21.1对8.0 mmHg，P < 0.01；13.7对8.6 mmHg，P < 0.01）。因此，25%MVC时收缩后的IMP高于70%MVC时（P < 0.01）。在两个MVC水平下，整个疲劳收缩过程中的IMP变化与f(mean)呈负相关，与RMS呈正相关；然而，这些相关性在25%MVC时更好。肌肉内水分积累的程度被讨论为25%和70%MVC之间IMP变化差异的主要原因。高收缩水平与低收缩水平之间所有参数变化率的显著差异可能表明存在一种共同机制，控制着IMP和EMG疲劳指标的变化。
