Affiliations: [a] Motor Control and Biomechanics Laboratory, Department
of Kinesiology, University of New Hampshire, Durham, NH, USA | [b] Department of Electrical Engineering, University of
New Hampshire, Durham, NH, USA | [c] Department of Sport Science and Physical Education,
University of Georgia, Athens, GA, USA
Note: [] Address for correspondence: Ronald V. Croce, Ph.D., Department
of Kinesiology, University of New Hampshire, Durham, NH 03824, USA. Tel.: +1
603 862 2080; Fax: +1 603 862 0154; E-mail: rvc@unh.edu
Abstract: The effect of contraction intensity (100%-, 75%-, 50%-, and
25%-maximum voluntary contraction [MVC]) and movement velocity (0°,
100°, 200°, 300°, and 400°/s) on the root mean square amplitude
(SEMG-RMS) and median frequency power spectrum (SEMG-MPF) of the surface
electromyography of the vastus medialis (VM) and rectus femoris (RF) muscles
during isokinetic extension movements was investigated. Eight healthy female
university students (age=23.1 ± 2.6 yrs., mean height=161.8 ± 6.8
cm, mean weight=64.6 ± 6.1 kg) with no known knee pathologies
participated in the study. Peak moment (PM), SEMG-MPF, and SEMG-RMS were
analyzed using separate repeated measures analysis of variance (ANOVA). Results
indicated (p⩽ 0.05): (1) an inverse relationship between PM and movement
velocity, which was consistent with the literature and the force-velocity
curve; (2) an increase in VM and RF SEMG-RMS across all isovelocity movements
compared to isometric, with highest values occurring at 200°/s; (2) a
linear increase in SEMG-RMS as force levels increased from 25%-MVC to 100%-MVC;
and, (3) an increase in SEMG-MPF values during isovelocity movements compared
to that found during isometric contractions, with highest values at 50°/s,
suggesting isovelocity movements facilitated a greater recruitment of
fast-twitch fibers. It appears that the degree to which the central nervous
system activates muscle is based on the interplay of both contraction intensity
and velocity needed to complete the required motor task.
