Insulin-like growth factor-2 genotype, fat-free mass, and muscle performance across the adult life span

1 Department of Kinesiology, College of Health and Human Performance, 4 Department of Animal & Avian Sciences, Biometrics Program, University of Maryland, College Park 20742; 2 National Institute on Aging, Gerontology Research Center, Baltimore, Maryland 21224; 3 Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania 15261; and 5 Division of Gerontology, University of Maryland School of Medicine, Baltimore Veteran's Affairs Medical Center, Baltimore, Maryland 21201 Submitted 11 September 2003 ; accepted in final form 3 August 2004 The influence of insulin-like growth factor-2 ( IGF2 ) genotype on total body fat-free mass (FFM), muscle strength, and sustained power (SP) was evaluated repeatedly at 2-yr intervals in two cohorts from the Baltimore Longitudinal Study of Aging. Cohort 1 was comprised of 94 men tested for isometric grip strength and SP. Cohort 2 was comprised of 246 men and 239 women tested for total body FFM and isokinetic peak torque. Subjects were retrospectively genotyped for the IGF2 gene's ApaI polymorphism. Differences between genotype groups for total FFM, strength, and SP at first visit, at peak age (35 yr), at age 65, and across the adult age span were analyzed using either two-sample t -tests or mixed-effects models, depending on the specific comparisons made. Isokinetic arm strength at the time of first visit was lower in A/A men than in G/G men ( P < 0.05). Compared with G/G women, A/A women had lower total body FFM, lower isokinetic arm and leg strength at the time of first visit, and lower values at age 35 (all P < 0.05) for these muscle phenotypes. Furthermore, this difference between the genotype groups was maintained at age 65 and across the adult age span ( P < 0.05). No genotype-associated differences in rates of loss of grip strength or SP were found in cohort 1 . These results from cohort 2 support the hypothesis that variation within a gene known to influence developing muscle affects muscle mass and muscle function in later life. muscle mass; muscle strength; muscle power; genetics; gender Address for reprint requests and other correspondence: B. F. Hurley, Dept. of Kinesiology, Univ. of Maryland, College Park, MD 20742 (E-mail: benhur{at}umd.edu )