Bilodeau M, Arsenault A B, Gravel D, Bourbonnais D
School of Rehabilitation, University of Montreal, Quebec, Canada.
Eur J Appl Physiol Occup Physiol. 1990;61(5-6):461-6. doi: 10.1007/BF00236068.
It has been proposed that the mean power frequency (MPF) of the electromyogram (EMG) power spectrum increases gradually with force of contraction and that this increase is a function of the fiber-type content of the muscle investigated and the inter-electrode distance (IED) used when recording the EMG signals. In order to test these hypotheses, the values of the MPF of two elbow extensor muscles, triceps brachii (TB, 65% fast twitch fibers) and anconeus (AN, 65% slow twitch fibers), were compared at different levels of contraction. Subjects (n = 13) produced ten static ramp elbow extensions [0-100% maximum voluntary contraction (MVC)]. EMG signals of each muscle were recorded with two pairs of surface miniature electrodes having IEDs of 6 mm and 30 mm respectively. MPFs were obtained at each of the following levels: 10, 20, 40, 60, 80 and 100% MVC. Statistical analyses indicated that the MPF of AN increased significantly (P less than 0.05) up to 60% MVC. In contrast, the MPF values for TB showed no significant change across different levels of contraction (P greater than 0.05). Since skinfold was on average 3.2 times thicker over TB than over AN it is suggested that the low-pass filtering effect of the skin could have prevented the observation of an increase of the MPF for TB. It thus appears that changes of the MPF with the level of force, as disclosed by surface electrode recordings, is specific to each muscle. Consequently one has to account for factors such as thickness of the skinfold when it comes to the determination of the fiber-type content of different muscles within a subject.
有人提出，肌电图（EMG）功率谱的平均功率频率（MPF）会随着收缩力的增加而逐渐升高，并且这种升高是所研究肌肉的纤维类型组成以及记录EMG信号时所用的电极间距（IED）的函数。为了验证这些假设，在不同收缩水平下比较了两块肘伸肌，即肱三头肌（TB，65%快肌纤维）和肘肌（AN，65%慢肌纤维）的MPF值。受试者（n = 13）进行了十次静态斜坡式肘伸展[0 - 100%最大自主收缩（MVC）]。分别用两对表面微型电极记录每块肌肉的EMG信号，电极间距分别为6 mm和30 mm。在以下每个水平获取MPF值：10、20、40、60、80和100%MVC。统计分析表明，AN的MPF在达到60%MVC之前显著增加（P小于0.05）。相比之下，TB的MPF值在不同收缩水平下没有显著变化（P大于0.05）。由于TB上方的皮褶平均比AN上方厚3.2倍，因此有人认为皮肤的低通滤波效应可能阻止了观察到TB的MPF增加。因此，表面电极记录所揭示的MPF随力水平的变化似乎因肌肉而异。因此，在确定受试者体内不同肌肉的纤维类型组成时，必须考虑诸如皮褶厚度等因素。
