Effect of step and ramp static contractions on the median frequency of electromyograms of back muscles in humans

被引:15
作者
Larivière, C
Arsenault, AB
Gravel, D
Gagnon, D
Loisel, P
机构
[1] Univ Montreal, Sch Rebahil, Montreal, PQ H3C 3J7, Canada
[2] Previcap, Longueuil, PQ J4K 5G4, Canada
[3] Univ Sherbrooke, Dept Kinanthropol, Sherbrooke, PQ J1K 2R1, Canada
[4] Univ Sherbrooke, Fac Med, Dept Surg, Sherbrooke, PQ J1K 2R1, Canada
关键词
electromyography; power spectrum analysis; back muscles; median frequency; ramp and step contractions;
D O I
10.1007/s004210100475
中图分类号
Q4 [生理学];
学科分类号
071003 ;
摘要
The purpose of this study was to compare the electromyogram median frequency (MF) values from two contraction modes (ramp vs step) at different force levels of eight back muscles. A group of 20 healthy male subjects stood in a dynamometer with the trunk in a vertical position and performed trunk extension contractions using the displayed L5/S1 extension moment as visual feedback. The electromyogram (EMG) signals from four pairs of back muscles were collected at 4.096 Hz using active surface electrodes during two 7 s static ramp contractions ranging from 0% to 100% of the maximal voluntary contraction (MVC) and two 5 s static step contractions performed at five forces (10%, 20%, 40%, 60% and 80% MVC). The root mean square (RMS) and MF of the EMG signals corresponding to 250 ins windows were computed at each force level for both contraction modes. The RMS from the ramp contractions were significantly higher than from the step contractions in six muscles. The corresponding MF showed a significant (alpha =0.05) contraction modexforce interaction in four muscles. A significant contraction mode main effect was obtained in four muscles having higher MF during step than during ramp contractions. These differences were more obvious (10-15 Hz) and more frequent at the lower (10%, 20% and 40% MVC) forces. It was suggested that mechanisms not related to motor unit recruitment mi-ht influence MF in contraction modes. These unknown mechanisms contaminate any possible relationship between the MF measurements and muscle composition.
引用
收藏
页码:552 / 559
页数:8
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