Influence of sex differences and knee joint position on electrical stimulation-modulated strength increases

This study examined the influence of sex differences and knee joint position on the effectiveness of isometric electrical stimulation in improving isometric and isokinetic strength. Twenty-seven females and 28 male subjects were assigned to either a control group (C) that received no electrical stimulation, to an experimental group that received stimulation of the quadriceps with the knee flexed at 65 degrees (EF), or to an experimental group that received electrical stimulation of the quadriceps with the knee fully extended (EE). Experimental subjects received 15 min of electrical stimulation 3 times/wk for a total of 6 wk. Before and after the study, knee extension strength was measured with a Cybex II, isometrically at 65 degrees of knee flexion and isokinetically at 30 degrees . s-1, 60 degrees . s-1, 90 degrees . s-1, and 120 degrees s-1. Multivariate analysis of covariance, using the pretests as the covariate, revealed no sex differences in responsiveness to electrical stimulation. EF was superior to EE at 30 degrees . s-1 and 120 degrees . s-1 in females and at 120 degrees . s-1 in males (P less than 0.05). Male and female EF was superior to C in all tests. EE was higher than C at isometric, 30 degrees . s-1, 90 degrees . s-1, and 120 degrees . s-1 in females and at isometric and 30 degrees . s-1 in males. These data suggest that electrical stimulation at the quadriceps can increase isometric and isokinetic strength and may be more effective in improving isokinetic strength if the knee is flexed during treatment.