Insulin-like growth factor 1 genotype and muscle power response to strength training in older men and women

Purpose: To determine if the IGF1 (CA) 19 repeat polymorphism influences muscle power at baseline and in response to strength training (ST) in older adults. Methods: Knee extensor (KE) peak power (PP) was measured at 50, 60, and 70% of 1 RM strength before and after 10 wks of unilateral KE ST in older adults, aged 50-85 yr., to determine the changes in absolute and relative PP with ST. Subjects (N = 114) were genotyped for the IGF1 CA repeat polymorphism and grouped as homozygous for the 192 allele, heterozygous, or non-carriers of the 192 allele. However, sample sizes varied substantially among the various dependent variables. Differences in baseline PP and changes with ST among genotype groups were determined using ANCOVA (covariates include: age, sex, baseline fat-free mass). Results: The 192 homozygotes had significantly lower baseline PP at 50%, 60%, and 70% of 1-RM strength than the non-carriers when age, sex and baseline fat-free mass was covaried. This same relationship was observed when the highest PP within these ranges was compared. Both absolute and relative PP increased significantly with ST in all genotype groups as expected, but there were no significant relationships between IGF1 genotype and any of the PP changes. Conclusion: Despite a significant relationship between IGF1 genotype and knee extensor peak power at baseline, IGF1 genotype does not appear to influence changes in knee extension peak power with ST