Pincivero D M, Campy R M, Salfetnikov Y, Bright A, Coelho A J
Human Performance and Fatigue Laboratory, Department of Physical Therapy, Eastern Washington University, Cheney, Washington 99004, USA.
J Appl Physiol (1985). 2001 Mar;90(3):804-10. doi: 10.1152/jappl.2001.90.3.804.
The purpose of this study was to assess the effects of contraction intensity, gender, and muscle on median frequency of the three superficial portions of the quadriceps femoris muscle. Thirty healthy volunteers were assessed for isometric electromyogram activity of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscles with the knee at 60 degrees flexion. Subjects performed 5-s isometric contractions at 10, 20, 30, 40, 50, 60, 70, 80, and 90% of the average of three maximal voluntary contractions. Median frequency (f(med)) of the three muscles was assessed through a power spectral analysis performed over 11 consecutive 512-ms epochs overlapping each other by one-half their length. The f(med) for each of the 11 epochs was then determined, followed by calculation of the mean and SD. The major findings of this study demonstrated that overall f(med) was significantly highest for the VL and lowest for the VM, whereas RF f(med) was between that of the other two muscles. Similar findings were observed for f(med) variability as the VL was significantly higher than the VM and RF, with no gender differences or differences between the latter two muscles. The results demonstrate that the largest change in f(med) as a function of contraction intensity occurred for the VL in men (18.6%) and women (7.6%). These findings suggest that muscle fiber-type homogeneity may exist in the VM and RF, which displayed negligible changes in f(med), whereas the VL may possess greater morphological variability.
本研究的目的是评估收缩强度、性别和肌肉对股四头肌三个浅表部分中位频率的影响。对30名健康志愿者在膝关节屈曲60度时进行股内侧肌（VM）、股外侧肌（VL）和股直肌（RF）的等长肌电图活动评估。受试者以三次最大自主收缩平均值的10%、20%、30%、40%、50%、60%、70%、80%和90%进行5秒等长收缩。通过对连续11个相互重叠一半长度的512毫秒时段进行功率谱分析，评估三块肌肉的中位频率（f(med)）。然后确定11个时段中每个时段的f(med)，接着计算平均值和标准差。本研究的主要发现表明，总体而言，VL的f(med)显著最高，VM的最低，而RF的f(med)介于其他两块肌肉之间。对于f(med)变异性也观察到类似的结果，因为VL显著高于VM和RF，性别之间以及后两块肌肉之间没有差异。结果表明，作为收缩强度函数的f(med)最大变化在男性（18.6%）和女性（7.6%）的VL中出现。这些发现表明，VM和RF中可能存在肌纤维类型同质性，其f(med)变化可忽略不计，而VL可能具有更大的形态变异性。
