The broad aim of this work is to understand the unique interactions of two distinct biological processes, human development and physical exercise, each of which is characterized by tissue plasticity. The general hypothesis is that endurance exercise training can modulate tissue growth by functional increases in growth hormone (GH) and/or by increased bioavailability of the insulin-like growth factors (IGF-I and II). The GH effect may be mediated by: 1) acute increases in GH following brief exercise; 2) increases in the frequency or amplitude of spontaneous GH pulses consequent to training; and/or 3) training effects on circulating GH binding protein (BP) suggesting alteration in GH tissue receptors. The IGF effects may be mediated by GH-related increases in circulating IGFs and/or by increased circulating IGF resulting from an exercise-associated IGFBP proteolysis. It is additionally hypothesized that the GH and IGF mechanisms that link physical activity and tissue growth are profoundly influenced by diet, gender and maturational state. Studies will be done in pre- and late pubertal children and in adults using diet intervention, training programs, magnetic resonance techniques, stable isotope assessment of energy expenditure, and state of the art assessments of circulating growth factors and their binding proteins.
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