UNLABELLED: The contributions of systemic versus local insulin-like growth factor-I (IGF-I) action for mediating fat-free mass (FFM) accretion have yet to be fully clarified, but circulating IGF-I is the preferred measure in clinical practice, and its merits as a biomarker have been demonstrated for a number of physiological outcomes. PURPOSE: To test the hypothesis that bioavailable IGF-I would have a stronger association with physical activity-induced FFM accretion than total IGF-I and would serve as a prognostic indicator of FFM accretion. METHODS: Seventy-seven young healthy women (21 ± 5 yr, 62.7 ± 8.5 kg, 27.0% ± 6.0% body fat) participated in 8 wk of Army basic training involving intense physical activity. Total and bioavailable IGF-I; IGF binding proteins (IGFBP) 1, 2, 3, 4, 5, and 6; and body composition parameters were measured before and after the training. RESULTS: There were significant (P≤0.05) increases in FFM (6%) and decreases in fat mass (-13%). Total IGF-I and IGFBP-4 to -6 increased, whereas IGFBP-1 and IGFBP-2 decreased. Bioavailable IGF-I (24%) explained three times the amount of variance in relative FFM changes than did total IGF-I (8%). Receiver operator characteristic curve analysis revealed that women with lower baseline bioavailable IGF-I were twice as likely to experience FFM gains >7%. Women gaining >7% FFM had greater increases in total IGF-I, maintained bioavailable IGF-I concentrations and experienced greater decreases in IGFBP-2 and increases in IGFBP-6 than those women gaining <7% FFM. CONCLUSIONS: Circulating bioavailable IGF-I has a moderate association with physical activity-induced increases in FFM accretion in young, healthy women, and this association is greater than observed for total IGF-I.
UNLABELLED: The contributions of systemic versus local insulin-like growth factor-I (IGF-I) action for mediating fat-free mass (FFM) accretion have yet to be fully clarified, but circulating IGF-I is the preferred measure in clinical practice, and its merits as a biomarker have been demonstrated for a number of physiological outcomes. PURPOSE: To test the hypothesis that bioavailable IGF-I would have a stronger association with physical activity-induced FFM accretion than total IGF-I and would serve as a prognostic indicator of FFM accretion. METHODS: Seventy-seven young healthy women (21 ± 5 yr, 62.7 ± 8.5 kg, 27.0% ± 6.0% body fat) participated in 8 wk of Army basic training involving intense physical activity. Total and bioavailable IGF-I; IGF binding proteins (IGFBP) 1, 2, 3, 4, 5, and 6; and body composition parameters were measured before and after the training. RESULTS: There were significant (P≤0.05) increases in FFM (6%) and decreases in fat mass (-13%). Total IGF-I and IGFBP-4 to -6 increased, whereas IGFBP-1 and IGFBP-2 decreased. Bioavailable IGF-I (24%) explained three times the amount of variance in relative FFM changes than did total IGF-I (8%). Receiver operator characteristic curve analysis revealed that women with lower baseline bioavailable IGF-I were twice as likely to experience FFM gains >7%. Women gaining >7% FFM had greater increases in total IGF-I, maintained bioavailable IGF-I concentrations and experienced greater decreases in IGFBP-2 and increases in IGFBP-6 than those women gaining <7% FFM. CONCLUSIONS: Circulating bioavailable IGF-I has a moderate association with physical activity-induced increases in FFM accretion in young, healthy women, and this association is greater than observed for total IGF-I.
Authors: Jess A Gwin; Adrienne Hatch-McChesney; Kenneth P Pitts; Rory P O'Brien; Anthony J Karis; Christopher T Carrigan; James P McClung; J Philip Karl; Lee M Margolis Journal: Physiol Rep Date: 2022-07
Authors: Lee M Margolis; Stefan M Pasiakos; J Philip Karl; Jennifer C Rood; Sonya J Cable; Kelly W Williams; Andrew J Young; James P McClung Journal: Nutrients Date: 2012-12-18 Impact factor: 5.717