HABITUAL EXERCISE DOES NOT PREVENT THE AGE-ASSOCIATED DECLINE IN GROWTH HORMONE/INSULIN LIKE GROWTH FACTOR-I 25

Abstract

Human aging is associated with a decline in secretion of growth hormone and insulin like growth factor-I (GH/IGF-I), which has been proposed to contribute to the observed somatic changes in older people. This decline in GH/IGF-I may be due to aging per se or to a reduction in physical activity that also commonly occurs with age. Acute exercise is known to stimulate GH secretion. To determine if habitual exercise prevents or retards age associated changes in GH/IGF-1 status or body composition and muscle strength, we compared 15 masters runners (Active, A) with 15 sedentary men (Non-Active, NA), aged 60 - 70 yrs. Maximal oxygen uptake (VO2 max) assessed by treadmill testing was higher in A than NA (40.0 ± 1.9 vs. 27.3 ± 1.4 ml/kg/min, mean ± SEM, P < 0.001). There was no difference in lean body mass, regional or whole body bone mineral density, but NA had higher (P < 0.05) body weight (73.8 ± 1.8 vs. 84.8 ± 4.0 kg), fat mass (12.8± 0.8 vs. 20.3 ± 2.2 kg) and percent fat (23.2 vs. 17.2) than A as assessed by DXA (Hologic 1000/W). Total IGF-I (A, 129 ± 10 ng/mL vs. NA, 124 ± 11 ng/mL) and the ratio IGF-1:IGFBP3, an index of bioavailable IGF-1 (A, 0.046 vs. NA, 0.048) were similar between goups. Concentric muscle strength (1-RM) for 8 upper and lower body muscle groups was comparable except for knee extension, where A were higher than NA (P < 0.05). With groups combined, there was no relationship between total or bioavailable IGF-I and any body composition or muscle strength variable. Conclusions: These results indicate that even high levels of endurance exercise do not prevent the decline in GH/IGF-I that occurs with normal human aging, and that neither total or bioavailable IGF-I predicts somatic status or muscle strength in healthy older men.