ACCURACY AND VARIABILITY OF LEG VELOCITIES DURING CONCENTRIC AND ECCENTRIC ACTIONS OF THE QUADRICEPS FEMORIS MUSCLES

This study examined the ability to control leg velocities during conce ntric and eccentric actions of the right quadriceps muscles. Ten healt hy women (M age = 25.9 +/- 3.5 yr.) were tested using the Isotonic Pro gram of the KIN-COM II 500H dynamometer. They attempted to match veloc ity tracings of 10 degrees, 20 degrees, and 40 degrees/sec. through 70 degrees of knee range of motion at a load equal to 10% of their maxim al mean concentric force. The actual mean velocities, mean percent dev iation from the target velocities, and the coefficient of variation fo r both actions were calculated for 15 degrees-75 degrees (full range o f motion), 15 degrees-45 degrees (shorter range of motion), and 46 deg rees-75 degrees (longer range of motion). Separate one-way analyses of variance with two trial factors (action x velocity) showed faster con centric velocities through the full and longer ranges of mot ion, and faster eccentric velocities through the shorter range of motion. Mean per cent deviations indicated that the eccentric velocities were gener ally more accurate within all ranges of motion. Larger concentric coef ficients of variation were found within the full and longer ranges of motion, and the coefficients of variation for both actions decreased a s the velocities increased. An exaggerated 'velocity overshoot' at the onset of both actions probably contributed to differences in the velo cities and coefficients of variation. The results indicated difference s between the concentric and eccentric actions, explained in part by t he testing methodology used and by the known mechanical and physiologi cal characteristics of the two muscle actions.