Increased physical activity and the growth hormone-IGF-I axis in adolescent males

Abstract

Insulin-like growth factor-I (IGF-I) is associated with muscle hypertrophy, and circulating IGF-I levels are correlated with fitness. To test the hypothesis that IGF-I increases with increased physical activity in adolescent males, 38 subjects (16 ± 0.7 yr old) were randomized to control ( n = 18) or increased physical activity groups for 5 wk. Before and after the intervention, we measured thigh muscle volume using magnetic resonance imaging and serum levels of mean growth hormone (GH) by overnight multiple sampling, GH binding protein (GHBP), IGF-I, and IGFBPs 1–5 by standard assays. Energy expenditure was assessed with the doubly labeled water technique toward the end of the study. In the training subjects there was 1) a significant increase in thigh muscle volume (+3.6 ± 1%), 2) 15.5 ± 3.3% greater energy expenditure than in controls, and 3) no evidence of weight loss (+1.44 ± 0.4%). In contrast to our hypothesis, but similar to our recent observations in adolescent females, training decreased IGF-I (−12 ± 4%, P < 0.005). Moreover, training substantially reduced GHBP (−21 ± 4%, P < 0.00002) and increased IGFBP-2 (+40 ± 16%, P < 0.008). Brief training increased muscle volume in weight-stable adolescent males and, surprisingly, influenced not only IGF-I but GHBP and IGFBP-2 as well in a manner typically found in energy-deficient states.

The Effect of Endurance-Type Exercise Training on Growth Mediators and Inflammatory Cytokines in Pre-Pubertal and Early Pubertal Males

“…Exercise training is linked to anabolic function through this axis, as previous cross-sectional studies from this and other groups have demonstrated that GH pulsatility and circulating IGF-I are higher in fitter adolescents and adults (2)(3)(4)(5). In contrast, we have consistently demonstrated a decrease in circulating elements of the GH-IGF-I axis in postpubertal males and females and in prepubertal girls in response to aerobic exercise (6,7). This was surprising for two reasons: first, because the training regimen led to significant increases in muscle mass and fitness without weight loss; and secondly, because IGF-I is known to be correlated with fitness in adults and adolescents, indicating a training-associated enhancement of anabolic activity (3)(4)(5).…”

Increased Plasma Levels of Growth Hormone, Insulin-Like Growth Factor (IGF)-I and IGF-Binding Protein 3 in Pregnant Rats with Exercise

“…Several authors have described an increase in plasma IGF-I after endurance training (Poehlman et al 1994;Koziris et al 1999), but others have reported an opposite effect (Eliakim et al 1996(Eliakim et al , 1998.…”

Physical activity and risk of renal cell cancer

“…Possible direct actions of physical activity include effects on plasma levels of insulin and insulin-like growth factors (IGF). A sedentary life might lead to higher levels of these hormones [11][12][13] that both could contribute to the growth, proliferation or metabolism of renal cell cancer. 14 Epidemiological studies indicate that patients with diabetes, which is associated with higher plasma insulin levels, have an increased risk of renal cell cancer.…”