TY - JOUR
T1 - Increased physical activity and the growth hormone-IGF-I axis in adolescent males
AU - Eliakim, Alon
AU - Brasel, Jo Anne
AU - Mohan, Subburaman
AU - Wong, Wai Lee T.
AU - Cooper, Dan M.
PY - 1998/7
Y1 - 1998/7
N2 - 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.
AB - 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.
KW - Binding proteins
KW - Energy expenditure
KW - Insulin-like growth factor-I
KW - Magnetic resonance imaging
KW - Muscle volume
UR - http://www.scopus.com/inward/record.url?scp=0031870556&partnerID=8YFLogxK
U2 - 10.1152/ajpregu.1998.275.1.r308
DO - 10.1152/ajpregu.1998.275.1.r308
M3 - ???researchoutput.researchoutputtypes.contributiontojournal.article???
C2 - 9688993
AN - SCOPUS:0031870556
SN - 0363-6119
VL - 275
SP - R308-R314
JO - American Journal of Physiology - Regulatory Integrative and Comparative Physiology
JF - American Journal of Physiology - Regulatory Integrative and Comparative Physiology
IS - 1 44-1
ER -