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Med Sci Sports Exerc. 2011 May;43(5):793-9. doi: 10.1249/MSS.0b013e31820065ea.

Bioavailable IGF-I is associated with fat-free mass gains after physical training in women.

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Military Performance Division, US Army Research Institute of Environmental Medicine, Natick, MA 01760, USA.


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.


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.


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.


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.


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.

[Indexed for MEDLINE]

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