Gerdle B, Elert J
Department of Physical Medicine and Rehabilitation, University of Umeå, Sweden.
Int J Sports Med. 1994 Jan;15 Suppl 1:S32-7. doi: 10.1055/s-2007-1021107.
The study investigated the temporal occurrence of the mean power frequency shift (MPF) of the EMG during prolonged (dynamic and static) working cycles. Ten healthy subjects took part in the experiment. The experimental protocol required each subject to first complete 70 maximum isokinetic knee extensions at 90 degrees s-1). Without any rest, the subject then performed a maximum static knee extension with the dynamometer positioned at 45 degrees of flexion until subjective exhaustion. This sequence of dynamic and static exercise was repeated two more times with a 5-min rest interval preceding each sequence. The EMG signal of the rectus femoris was obtained simultaneously with the torque signal (PT) from the dynamometer. Dynamic contractions PT and MPF decreased throughout the three dynamic periods. Patterns composed of two phases were found; first an initial steep decrease during the first 40 contractions followed by a less steep decrease. Static contractions PT decreased significantly during the three static contractions. Significant (small) decreases in MPF occurred only during the second and third static contractions. Since the major part of the MPF shift occurred early in the exhaustive performance, it is questioned whether the MPF shift detects peripheral fatigue of the type 1 fibers.
该研究调查了在长时间（动态和静态）工作周期中肌电图平均功率频率偏移（MPF）的时间发生情况。十名健康受试者参与了实验。实验方案要求每名受试者首先以90度/秒的速度完成70次最大等速膝关节伸展。在没有任何休息的情况下，受试者随后使用测力计将其定位在45度屈曲位置进行最大静态膝关节伸展，直到主观疲劳。这种动态和静态运动的序列再重复两次，每个序列之前有5分钟的休息间隔。股直肌的肌电图信号与测力计的扭矩信号（PT）同时获得。在三个动态阶段中，动态收缩时的PT和MPF均下降。发现了由两个阶段组成的模式；首先在最初的40次收缩期间出现最初的急剧下降，随后下降幅度较小。在三次静态收缩期间，静态收缩时的PT显著下降。仅在第二次和第三次静态收缩期间，MPF出现显著（微小）下降。由于MPF偏移的主要部分在力竭运动早期出现，因此有人质疑MPF偏移是否能检测出1型纤维的外周疲劳。
