Mechanomyographic responses to concentric isokinetic muscle contractions

The purpose of this investigation was to examine the effects of velocity of contraction on the mechanomyographic (MMG) responses to maximal concentric isokinetic leg extension movements. Eight adult males [mean (SD) age, 22.3 (1.3) years] performed maximal leg extensions on a calibrated Cybex 6000 dynamometer at velocities of 60, 120, 180, 240, 300, and 360 degrees x s(-1) x MMG responses were detected by a piezoelectric recording device placed over the vastus lateralis muscle. Intraclass reliability correlations ranged from R = 0.84 to 0.97 and from 0.90 to 0.99 for peak torque and MMG amplitude values, respectively, with no significant differences (P > 0.05) between the mean values for test versus retest at any contraction velocity. There were significant differences (P < 0.05) in peak torque at all velocities except 240 [135 (27) Nm] versus 300 [127 (27) Nm], and 300 versus 360 degrees x s(-1) [115 (37) Nm]. The mean MMG amplitude at 60 degrees x s(-1) [61 (67) mV] was significantly less (P < 0.05) than that at 360 degrees x s(-1) [452 (451) mV]. These results indicate a velocity-related dissociation between MMG amplitude and peak torque. Furthermore, it was hypothesized that the increases in MMG amplitude were due to velocity-related decreases in muscle stiffness which allowed for greater muscle fiber oscillations.