Abstract
Previous investigations have examined the effect of gravity correction on hamstring and quadriceps force and reciprocal muscle group ratios when tested from a seated position. The effect of gravity correction on these values when knee extension is tested from supine and knee flexion from prone has not been determined. This study tested 48 females for concentric and eccentric average force of the quadriceps in the supine position and of the hamstring muscle group in the prone position with a Kin Com dynamometer. For the quadriceps and hamstring muscle groups, the gravity-corrected values were greater (p < .01) than gravity-uncorrected values for concentric and eccentric force. The gravity-corrected flexion/extension reciprocal muscle group ratios were also greater (p < .01) than uncorrected ratios when determined from both concentric and eccentric average force values. These findings indicate gravity correction had a significant effect on both quadriceps and hamstring force production and reciprocal muscle group ratios, regardless of the fact that both muscle groups were assessed against the effects of gravity. Furthermore, the effect of gravity correction on the hamstring muscle group was approximately twice as great as on the quadriceps. These findings support the need to correct for the effect of gravity when assessing knee extension from supine and knee flexion from prone. Thus, it is very important for clinicians to report how testing and gravity correction were accomplished to allow proper interpretation and analysis of the presented values.