Häkkinen K, Komi P V
Electroencephalogr Clin Neurophysiol. 1983 Apr;55(4):436-44. doi: 10.1016/0013-4694(83)90132-3.
Effects of fatigue produced by a maintained 50% isometric loading on electromyographic (EMG) and mechanical characteristics of voluntary and reflex contractions of human skeletal muscles were studied in 14 males. A continuous isometric loading of the knee extensors caused significant (P less than 0.001) increase in integrated EMG (IEMG) and decrease (P less than 0.001) in mean power frequency (MPF) of the EMG spectrum. The decrease in MPF was related (P less than 0.05) to percentage fast twitch (FT) fibre area of the vastus lateralis muscle. In reflexly induced contractions no changes were observed during fatigue in reflex latency (LAT) but electromechanical delay (EMD) increased significantly (P less than 0.01). The decrease in voluntary MPF and increase in reflex EMD were interrelated (P less than 0.05). Fatigue loading increased (P less than 0.05) the peak-to-peak amplitude of EMG of the reflex contraction but decreased (P less than 0.01) the corresponding force amplitude. The increase (P less than 0.01) in this reflex EMG/force ratio was related (P less than 0.05) to the corresponding increase observed in IEMG/force ratio of the voluntary contraction. The present findings support the differential fatiguing properties of fast twitch and slow twitch muscle fibres. In addition the fatigue effects on reflexly induced contractions show that fatigue took place primarily in the contractile processes and that muscle spindle sensitivity was increased during fatigue loading.
在14名男性中研究了持续50%等长负荷产生的疲劳对人体骨骼肌随意收缩和反射性收缩的肌电图（EMG）及力学特性的影响。膝关节伸肌的持续等长负荷导致EMG积分（IEMG）显著增加（P<0.001），EMG频谱的平均功率频率（MPF）降低（P<0.001）。MPF的降低与股外侧肌快肌纤维（FT）面积百分比相关（P<0.05）。在反射性诱发的收缩中，疲劳期间反射潜伏期（LAT）未观察到变化，但机电延迟（EMD）显著增加（P<0.01）。随意MPF的降低和反射EMD的增加相互关联（P<0.05）。疲劳负荷增加了反射性收缩EMG的峰峰值幅度（P<0.05），但降低了相应的力幅度（P<0.01）。这种反射EMG/力比值的增加（P<0.01）与随意收缩的IEMG/力比值中观察到的相应增加相关（P<0.05）。目前的研究结果支持快肌纤维和慢肌纤维不同的疲劳特性。此外，疲劳对反射性诱发收缩的影响表明，疲劳主要发生在收缩过程中，并且在疲劳负荷期间肌梭敏感性增加。
