Bilodeau M, Arsenault A B, Gravel D, Bourbonnais D
School of Rehabilitation, Faculty of Medicine, University of Montreal, Quebec, Canada.
Eur J Appl Physiol Occup Physiol. 1991;63(1):24-8. doi: 10.1007/BF00760796.
The goal of the present study was to compare electromyogram (EMG) power spectra obtained from step (constant force level) and ramp (progressive increase in the force level) isometric contractions. Data windows of different durations were also analysed for the step contractions, in order to evaluate the stability of EMG power spectrum statistics. Fourteen normal subjects performed (1) five ramp elbow extensions ranging from 0 to 100% of the maximum voluntary contraction (MVC) and (2) three stepwise elbow extensions maintained at five different levels of MVC. Spectral analysis of surface EMG signals obtained from triceps brachii and anconeus was performed. The mean power frequency (MPF) and the median frequency (MF) of each power spectrum were obtained from 256-ms windows taken at 10, 20, 40, 60 and 80% MVC for each type of contraction and in addition on 512-, 1024- and 2048-ms windows for the step contractions. No significant differences (P greater than 0.05) were found in the values of both spectral statistics between the different window lengths. Even though no significant differences (P greater than 0.05) were found between the ramp and the step contractions, significant interactions (P less than 0.05) between these two types of contraction and the force level were found for both the MPF and the MF data. These interactions point out the existence of different behaviours for both the MPF and the MF across force levels between the two types of contraction.
本研究的目的是比较从等长收缩的阶梯式（恒定力水平）和斜坡式（力水平逐渐增加）收缩中获得的肌电图（EMG）功率谱。还对阶梯式收缩不同持续时间的数据窗口进行了分析，以评估EMG功率谱统计数据的稳定性。14名正常受试者进行了：（1）五次从最大自主收缩（MVC）的0%到100%的斜坡式肘部伸展；（2）三次在五个不同MVC水平维持的阶梯式肘部伸展。对从肱三头肌和肘肌获得的表面肌电信号进行了频谱分析。对于每种类型的收缩，在10%、20%、40%、60%和80%MVC时，从256毫秒的窗口中获取每个功率谱的平均功率频率（MPF）和中位数频率（MF），此外，对于阶梯式收缩，还在512毫秒、1024毫秒和2048毫秒的窗口中获取。在不同窗口长度之间，两种频谱统计值均未发现显著差异（P大于0.05）。尽管在斜坡式收缩和阶梯式收缩之间未发现显著差异（P大于0.05），但对于MPF和MF数据，在这两种类型的收缩与力水平之间发现了显著的交互作用（P小于0.05）。这些交互作用表明，在两种类型的收缩中，MPF和MF在不同力水平上存在不同的行为。
