RELATIONSHIP OF CIRCULATING GROWTH HORMONE (GH), GH BINDING PROTEIN (BP), AND INSULIN-LIKE GROWTH FACTOR-I (IGF-I) TO PHYSICAL FITNESS AND MUSCLE MASS IN ADOLESCENT FEMALES. 512

While physical activity/inactivity affects local tissue growth (e.g., muscle, bone) there appears to be a more global neuroendocrine adaptation as well. Understanding this would be of particular relevance for childhood and adolescence when a variety of growth hormones are in flux. We examined the relationship between physical fitness and the GH→IGF-I axis [i.e., GH, GHBP, and IGF-I] in 23 healthy females (age range 15-17). We assessed physical fitness both by VO₂max (measured by cycle ergometery) and by muscle mass (thigh musculature, measured by magnetic resonance imaging) each normalized to body weight. Mean nocturnal GH was calculated from overnight values (12-hr). GH and IGF-I were assessed using RIA, and GHBP by ligand-mediated immunofunctional assay.

Results: Table Thus, structural and functional indexes of physical fitness are correlated with circulating components of the GH→IGF-I axis in adolescent females. This neuroendocrine adapation may play a role in the anabolic responses to exercise.

Table 1