Specific effects of eccentric and concentric training on muscle strength and morphology in humans

The purpose of this study was to compare pure eccentric and concentric isok inetic training with respect to their possible specificity in the adaptatio n of strength and morphology of the knee extensor muscles. Ten moderately t rained male physical education students were divided into groups undertakin g eccentric (ETG) and concentric (CTG) training. They performed 10 weeks of maximal isokinetic (90 degrees.s(-1)) training of the left leg, 4 x 10 rep etitions - three times a week, followed by a second 10-week period of simil ar training of the right-leg. Mean eccentric and concentric peak torques in creased by 18% and 2% for ETG and by 10% and 14% for CTG, respectively. The highest increase in peak torque occurred in the eccentric 90 degrees.s(-1) test for ETG (35%) whereas in CTG strength gains ranged 8%-15% at velociti es equal or lower than the training velocity. Significant increases in stre ngth were observed in the untrained contra-lateral leg only at the velocity and mode used in ipsilateral training. Cross-sectional area of the quadric eps muscle increased 3%-4% with training in both groups, reaching statistic al significance only in ETG. No major changes in muscle fibre composition o r areas were detected in biopsies from the vastus lateralis muscle for eith er leg or training group. In conclusion, effects of eccentric training on m uscle strength appeared to be more mode and speed specific than correspondi ng concentric training. Only minor adaptations in gross muscle morphology i ndicated that other factors, such as changes in neural activation patterns, were causing the specific training-induced gains in muscle strength.