RESISTANCE TRAINING AND THE GH/IGF-1 AXIS IN WOMEN

Declining levels of anabolic hormones such as growth hormone (GH) and insulin-like growth factor-1 (IGF-1) may exacerbate age-related losses of lean body mass and physical function in women. Exercise can stimulate the GH/IGF-1 axis, however, the response may be affected by age, estrogen levels, and training status. PURPOSE To examine the effect of resistance training on the GH and IGF-1 response to exercise in women of different ages and estrogen levels. METHODS 45 subjects were recruited: 16 postmenopausal women using supplemental estrogen (HRT), 16 postmenopausal women not using estrogen (NHRT), and 13 young, premenopausal women (YW). Subjects in each group were randomly selected into a 12-week resistance training program (RT) or a control group (C). At weeks 0 and 13, subjects completed 2 sets of 10 reps of 8 exercises at 10RM intensity. Preexercise, post-exercise and 15 minute recovery blood samples were analyzed for plasma lactate and serum levels of GH, IGF-1, and estradiol (E2). YW were tested in the early follicular phase of their menstrual cycle. Group, time, and week comparisons were made using repeated measures ANOVA. RESULTS Resting E2 levels were significantly different between all groups (p < 0.01) with HRT having the highest and NHRT having the lowest. Post-exercise lactate was significantly greater at week 13 compared to week 0 (p < 0.01). GH increased significantly in response to the exercise session (p < 0.01). Post-exercise GH concentrations did not differ between groups, however, the relative change after exercise was greater in the YW-RT group compared to all other groups (p < 0.05). IGF-1 concentrations showed a small but significant post-exercise increase (p < 0.01). The relative post-exercise change in IGF-1 was significantly greater after training (p < 0.05) however there were no systematic group differences in IGF-1 responses to exercise. CONCLUSION Training status and exercise intensity appear to have a greater effect than age of E2 levels on the relative GH and IGF-1 responses to exercise. Supported by the Medical Research Fund of NB and NSERC.