Effect of contraction intensity [100%, 75%, 50%, and 25% maximum voluntary contraction (MVC)] and movement velocity [0° (isometric)], 50°, 100°, 200°, and 400°/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 ≤ .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°/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° / sec. Isovelocity contractions were inferred to facilitate a greater recruitment of fast-twitch fibers (via increased SEMG–MNF), which was intensified at 50°/sec, whereas greater overall muscle activation was found at 200° / sec.
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