THE INFLUENCE OF ENDURANCE TRAINING ON INSULIN-LIKE GROWTH-FACTOR-I IN OLDER INDIVIDUALS

Previous cross-sectional studies have suggested that lower levels of insulin-like growth factor-1 (IGF-1) in older persons are related in part to diminished physical exercise. However, it is unknown whether the introduction of long-term exercise in previously inactive older individuals increases IGF-1, and whether the response is different between older men and women. Thus, we examined the effects of 8 weeks of endurance training on changes in IGF-1, IGF-1 binding protein-1 (IGFBP-1), IGFBP-3, and maximal aerobic power (Vo(2)max)in 18 older individuals (aged 66.1 +/- 1.4 years, 10 men and eight women). Individuals were also characterized for changes in body composition, estimated energy intake, and fasting plasma levels of glucose, insulin, and glucagon before and after an exercise training program. Endurance training increased Vo(2)max similarly in men (14%, P < .01) and women (14%,P < .01), but women showed a smaller increase in IGF-1 (8%, NS) than men (19%, P < .01). The correlation between changes in Vo(2)max and IGF-1 was significant in men (r = .79, P < .02), but not in women (r = .22, NS). Although no mean group change in IGFBP-1 or IGFBP-3 was noted, the individual changes between IGF-1 and IGFBP-3 showed a tendency to be related in men (r = .48, P = .15), but not in women (-.21, NS). Exercise training decreased plasma glucose (P < .05) in men, but not in women. No significant changes in fat-free mass, fat mass, and plasma insulin or glucagon in response to endurance training were noted in men or women. We conclude that endurance training increases fasting levels of IGF-1, and that this increase is more pronounced in older men than women. Copyright (C) 1994 by W.B. Saunders Company