Effect of age on muscle hypertrophy induced by resistance training.

BACKGROUND Previous research has shown that resistance training induces muscle hypertrophy in older subjects, but has not clarified whether the degree of hypertrophy is affected by age. The present study was done to test the hypothesis that men and women over 60 years old have a smaller hypertrophic response to resistance training than young adults. METHODS Cross-sectional areas (CSA) of muscle in the thigh and upper arm were determined before and after 3 months of progressive resistance training by magnetic resonance imaging (MRI) in 9 young (22-31 yr, 5 male and 4 female) and 8 old (62-72 yr, 4 male and 4 female) subjects. Strength was determined by 3-repetition-maximum (3RM) testing. The amount of weight lifted during the training program was proportional to baseline strength. RESULTS Mean pretraining 3RM strength, per cm2 CSA, was less in the older group for all muscle groups examined (16 +/- 6% for elbow flexors, p < .02; 40 +/- 7% for knee flexors, p < .001; 19 +/- 9% for knee extensors, p < .05). Mean training-induced increases in muscle CSA were less in the older group for elbow flexors (22 +/- 4% in young, 9 +/- 4% in old, p < .05) and knee flexors (8 +/- 2% in young, 1 +/- 2% in old, p < .01), but not for knee extensors (4 +/- 1% in young, 6 +/- 2% in old). Mean training-induced increases in specific tension (ratio of 3RM strength to CSA) were similar in young and old groups for elbow flexors (21 +/- 5% in young, 19 +/- 5% in old) and knee extensors (38 +/- 6% in young, 32 +/- 14% in old), but were greater in the older group for knee flexors (28 +/- 5% in young, 64 +/- 13% in old, p < .02). CONCLUSIONS Aging can attenuate the hypertrophic response of muscle groups to resistance training, when the training load is proportional to baseline strength. However, aging does not impair training-induced increases in specific tension.