EFFECT OF RECOMBINANT HUMAN GROWTH-HORMONE ON THE MUSCLE STRENGTH RESPONSE TO RESISTANCE EXERCISE IN ELDERLY MEN

Normal aging is characterized by detrimental changes in body compositi on, muscle strength, and somatotropic function. Reduction in muscle st rength contributes to frailty and risk for fracture in the elderly. Al though older adults increase muscle strength as a result of resistance exercise training, the strength gains quickly level off, with only mo dest increases thereafter despite continued training. To investigate w hether age-related deficits in the somatotropic axis limit the degree to which muscle strength can improve with resistance training in older individuals, we conducted a double blind, placebo-controlled exercise trial. Eighteen healthy elderly men (65-82 yr) initially underwent pr ogressive weight training for 14 weeks to invoke a trained state. Subj ects were then randomized to receive either 0.02 mg/kg BW.day recombin ant human GH (rhGH) or placebo, given sc, while undertaking a further 10 weeks of strength training. Sequential measurements were made of mu scle strength (one repetition maximum), body composition (dual energy x-ray absorptiometry), and circulating levels of insulinlike growth fa ctor-I (IGF-I) and IGF-binding protein-3. For each exercise, strength increased for both groups (P = 0.0001) through 14 weeks of training, w ith little improvement thereafter. Increases in muscle strength ranged from 24-62% depending on the muscle group. Baseline plasma IGF-I conc entrations were similar in both groups (mean +/- SEM, 106 +/- 9 mu g/L ), approximately half that observed in healthy young adults. In the rh GH group, IGF-I levels increased to 255 +/- 32 mu g/L at week 15 and 2 18 +/- 21 mu g/L at week 24 (P < 0.001). In the placebo group, IGF-I i ncreased slightly to 119 +/- 6 mu g/L at 24 weeks. IGF-binding protein -a also increased in the rhGH group (P < 0.05). rhGH had no effect on muscle strength at any time, and no systematic difference in muscle st rength was observed between groups throughout the study. Body weight d id not change in either group, but lean body mass increased, and fat m ass decreased (P < 0.05) in the rhGH group. Supplementation with rhGH does not augment the response to strength training in elderly men. The se results suggest that deficits in GH secretion do not underlie the t ime-dependent leveling off of muscle strength seen with training in th e elderly and provide no support for the popular view of GH as an ergo genic aid.