The effect of movement velocity and movement pattern on the reciprocal co-activation of the hamstrings.

The effect of velocity and movement pattern (reciprocal vs. non-reciprocal) on the reciprocal co-activation of the hamstrings was investigated through analysis of the root mean square (RMS) and the median frequency (MDF) of surface electromyography (SEMG). Fourteen subjects performed six continuous repetitions of a reciprocal isokinetic movement pattern (maximal extension followed by maximal flexion), and six continuous repetitions of a non-reciprocal movement pattern (maximal extension only) at 100 degrees, 200 degrees, 300 degrees s-1, and 400 degrees s-1. Data were analyzed using separate 2 x 4 (movement pattern x angular velocity) repeated measures analysis of variance (ANOVA). No significant differences (p > 0.05) were noted between reciprocal and non-reciprocal movement patterns for RMS. However, results did reveal a velocity effect for RMS (F = 5.0, p < 0.01), with significant differences observed between 100 degrees s-1 and 400 degrees s-1 (F = 9.4, p < 0.01), 200 degrees s-1 and 400 degrees s-1 (F = 9.5, p < 0.01), and 300 degrees s-1 and 400 degrees s-1 (F = 11.0, p < 0.001), with RMS values at 400 degrees s-1 being the highest. There was also a velocity effect for MDF (F = 8.03, p < 0.001), with significant differences observed between 100 degrees s-1 and 300 degrees s-1 (F = 4.2, p < 0.05), 100 degrees s-1 and 400 degrees s-1 (F = 20.2, p < 0.0001), 200 degrees s-1 and 400 degrees s-1 (F = 15.221, p < 0.001), and 300 degrees s-1 and 400 degrees s-1 (F = 5.9, p < 0.01). In all cases the highest MDF values were exhibited at the lower velocities. Lastly, there was an interaction effect when comparing movement patterns at 400 degrees s-1, with MDF values being significantly higher during the non-reciprocal movement pattern than during the reciprocal movement pattern (F = 10.9, p < 0.01). Results indicated that during isokinetic movements, RMS and MDF activity of the hamstrings are altered as velocity changes. More specifically, as velocity increases overall hamstrings' co-activation increases and there is a shift in the power spectrum toward the recruitment of slower-twitch muscle fibers. Results also indicate that movement pattern (reciprocal vs. non reciprocal) does not effect appreciably SEMG activity of hamstrings' co-contraction.