Effect of contraction type angular velocity and arc of motion on VMO : VL EMG ratio

This research was supported by a grant from the Walter P. Inman Fund through the Duke University Medical Research Council. Selected quadriceps muscle action may influence the movement path of the patella in the malaligned patellofemoral joint. The purpose of this study was to investigate the effects of arc of motion, angular velocity, and contraction type on the vastus medialis obliques:vastus lateralis (VMO:VL) absolute averaged electromyographic (AAEMG) ratio. Thirty healthy subjects performed maximum concentric and eccentric isokinetic quadriceps muscle contractions on the Kin-Com(R) dynamometer at velocities of 60 and 120 degrees /sec. Electromyography data from the VMO and the VL were acquired, and a VMO:VL AAEMG ratio was calculated for all combinations of the three independent variables. The results indicate that the VMO:VL AAEMG ratio for the 60 degrees -85 degrees arc was significantly greater than the ratio for the 35 degrees -60 degrees arc (p < 0.05), the ratio for the 60 degrees -85 degrees arc was significantly greater than the ratio for the 10 degrees -35 degrees arc (p < 0.05), and the ratio for the 35 degrees -60 degrees arc was significantly greater than the ratio for the 10 degrees -35 degrees arc (p < 0.05). The VMO:VL AAEMG ratio for concentric contraction at 120 degrees /sec was significantly greater than the ratio for concentric contraction at 60 degrees /sec (p < 0.05) and was significantly greater than the ratio for eccentric contraction at 120 degrees /sec (p < 0.05). The results indicate that the VMO:VL AAEMG ratio is affected by isokinetic exercise parameters. The use of isokinetic exercise parameters that produce a greater VMO:VL AAEMG ratio may be effective in altering muscular imbalance between the VMO and VL. J Orthop Sports Phys Ther 1991;14(6):256-262.