Physical fitness, endurance training, and the growth hormone-insulin-like growth factor I system in adolescent females.
We examined the relationship between physical fitness and circulating components of the GH-insulin-like growth factor I (IGF-I) system [i.e. GH, GH-binding protein (GHBP), IGF-I, and IGF-binding proteins 1-5 (IGFBP-1 through-5)] in adolescent females (age range, 15-17 yr). The study consisted of 1) a cross-sectional protocol (n = 23) in which GH-IGF-I components were correlated with fitness, as estimated by thigh muscle volume and maximal O2 uptake; and 2) a prospective study in which fitness, GH-IGF-I system components, and osteocalcin were examined before and after a 5-week period of endurance-type training (control, n = 6; trained, n = 10). The cross-sectional analysis revealed significant (P < 0.05) positive correlations between fitness and 1) mean 12-h overnight GH levels, 2) GHBP, and 3) IGF-I. Muscle volume was negatively correlated with both IGFBP-2 and -4. The prospective training study was associated with 1) increases in circulating osteocalcin (39 +/- 14%; P < 0.007), and 2) decreases in IGF-I (-14 +/- 5%; P < 0.05) and IGFBP-5 (-10 +/- 4%; P < 0.04). Unexpectedly, IGFBP-3 fell in both control (-8 +/- 2%; P < 0.01) and trained subjects (-5 +/- 3%; P < 0.05), and GHBP was reduced only among control subjects (-10 +/- 7%; P < 0.04). In summary, fitter adolescent girls tended to have increased mean serum GH, GHBP, and IGF-I. In contrast, brief endurance training led to increases in muscle mass and serum osteocalcin that were not accompanied by increases in GH or IGF-I. In fact, training may, in the short term, have led to a catabolic state hormonally expressed by reductions in IGF-I and IGFBP-5.
Eliakim
A
A
Department of Pediatrics, Harbor- University of California-Los Angeles Medical Center, Torrance 90509, USA.
Brasel
J A
JA
Mohan
S
S
Barstow
T J
TJ
Berman
N
N
Cooper
D M
DM
D000293:Adolescent; D002352:Carrier Proteins / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D019382:Human Growth Hormone / Q000097:blood*; D006801:Humans; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000033:anatomy & histology; D010806:Physical Education and Training; D010807:Physical Endurance / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology*; D011446:Prospective Studies
D002352:Carrier Proteins; D018975:Insulin-Like Growth Factor Binding Protein 5; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; C051815:somatotropin-binding protein