Effects of age, gender, and myostatin genotype on the hypertrophic response to heavy resistance strength training

Background. Because of the scarcity of data available from direct compariso ns of age and gender groups using the same relative training stimulus, it i s unknown whether older individuals can increase their muscle mass as much as young individuals and whether women can increase as much as men in respo nse to strength training (ST). In addition, little is known about whether t he hypertrophic response to ST is affected by myostatin genotype, a candida te gene for muscle hypertrophy. Methods, Eleven young men (25 +/- 3 years, range 21-29 years), 11 young wom en (26 +/- 2 years, range 23-28 years), 12 older men (69 +/- 3 years, range 65-75 years), and 11 older women (68 +/- 2 years, range 65-73 pears) had b ilateral quadriceps muscle volume measurements performed using magnetic res onance imaging (MRI) before and after ST and detraining. Training consisted of knee extension exercises of the dominant leg three times per week for 9 weeks. The contralateral limb was left untrained throughout the ST program . Following the unilateral training period, the subjects underwent 31 weeks of detraining during which no regular exercise was performed. Myostatin ge notype was determined in a subgroup of 32 subjects, of which five female su bjects were carriers of a myostatin gene variant. Results. A significantly greater absolute increase in muscle volume was obs erved in men than in women (204 +/- 20 vs 101 +/- 13 cm(3), p < .01), but t here was no significant difference in muscle volume response to ST between young and older individuals. The gender effect remained after adjusting for baseline muscle volume. In addition, there was a significantly greater los s of absolute muscle volume after 31 weeks of detraining in men than in wom en (151 +/- 13 vs 88 +/- 7 cm(3), p < .05), but no significant difference b etween young and older individuals.;Myostatin genotype did not explain the hypertrophic response to ST when all 32 subjects were assessed. However, wh en only women were analyzed, those with the less common myostatin allele ex hibited a 68% Larger increase in muscle volume in response to ST (p = .056) . Conclusions. Aging does not affect the muscle mass response to either ST or detraining, whereas gender does, as men increased their muscle volume abou t twice as much in response to ST as did women and experienced larger losse s in response to detraining than women. Young men were the only group that maintained muscle volume adaptation after 31 weeks of detraining. Although myostatin genotype may not explain the observed gender difference in the hy pertrophic response to ST, a role for myostatin genotype may be indicated i n this regard for women, but future studies are needed with larger subject numbers in each genotype group to confirm this observation.