Relative changes in maximal force, EMG, and muscle cross-sectional area after isometric training

The purpose of this experiment was to determine whether training-induced increases in maximal voluntary contraction (MVC) can be completely accounted for by increases in muscle cross-sectional area. Fifteen female university students were randomly divided into a control (N = 7) and an experimental (N = 8) group. The experimental group underwent 8 wk of isometric resistance training of the knee extensors of one leg; the other leg was the untrained control. Training consisted of 30 MVC.d-1 x 3 d.wk-1 x 8 wk. Extensor cross-sectional area (CSA), assessed by computerized tomographic (CT) scanning of a cross-sectional slice at mid-thigh, was used as a measure of muscle hypertrophy. After 8 wk of training, MVC increased by 28% (P < 0.05), CSA increased by 14.6% (P < 0.05), and the amplitude of the electromyogram at MVC (EMGmax) was unchanged in the trained leg of the experimental subjects. The same measures in the untrained legs of the experimental subjects and in both legs of the control subjects were not changed after training. Although there was an apparent discrepancy between the increase in MCV (28%) and CSA (14.6%), the ratio between the two, the specific tension (N.cm-2), was not significantly different after training. As a result of these findings, we conclude that in these subjects there is no evidence of nonhypertrophic adaptations to resistance training of this type and magnitude, and that the increase in force-generating capacity of the muscle is due to the synthesis of additional contractile proteins.