Contraction intensity and velocity on vastus lateralis SEMG power spectrum and amplitude.
Effect of contraction intensity [100%, 75%, 50%, and 25% maximum voluntary contraction (MVC)] and movement velocity [0 degrees (isometric)], 50 degrees, 100 degrees, 200 degrees, and 400 degrees/sec. [isovelocities]) on root mean square amplitude (SEMG-RMS) and median frequency power spectrum (SEMG-MNF) of vastus lateralis (VL) surface electromyography was investigated with ten healthy female university students. Peak torque (PT), mean torque (MT), SEMG-MNF, and SEMG-RMS, analyzed using separate repeated-measures analyses of variance (p < or = .05), indicated: (1) an inverse relation between PT and MT and movement velocity, (2) greater SEMG-MNF values during all isovelocity conditions compared with isometric conditions, with highest values occurring at 50 degrees /sec. and at 100% and 75% MVC, and (3) at all contraction intensities SEMG-RMS values were higher during dynamic movements than isometric movements and highest at 200 degrees /sec. Isovelocity contractions were inferred to facilitate a greater recruitment of fast-twitch fibers (via increased SEMG-MNF), which was intensified at 50 degrees /sec., whereas greater overall muscle activation was found at 200 degrees /sec.
Department of Kinesiology, University of New Hampshire, Durham 03824, USA. jm@unh.edu
John
J
Miller
Ronald
R
Croce
Michael
M
Horvat
Wayne
W
Smith
D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007719:Knee Joint / Q000502:physiology; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology; D052097:Quadriceps Muscle / Q000502:physiology*; D011999:Recruitment, Neurophysiological; D019415:Torque