Insulin-like Growth Factor 1 Genotype Influences Muscle Strength Response to Sterngth Training in Older Adults

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Strength training (ST) is considered an intervention of choice for the prevention and treatment of sarcopenia. The insulin-like growth factor 1 protein (IGF-I) plays a major role in ST-induced skeletal muscle hypertrophy and strength improvements. A microsatellite repeat in the promoter region of the IGF1 gene has been associated with IGF-I blood levels and phenotypes related to IGF-I in adult men and women. To examine the influence of this polymorphism on muscle hypertrophic and strength responses to strength training (ST), we studied 67 Caucasian men and women before and after a 10-week single leg knee extension ST program. One repetition maximum (1RM) strength, muscle volume (MV) via computed tomography (CT), and muscle quality (MQ) were assessed at baseline and after 10 weeks of training. The IGF1 repeat promoter polymorphism and three single nucleotide polymorphisms (SNP) were genotyped. For the promoter polymorphism, subjects were grouped as homozygous for the 192 allele, heterozygous, or non-carriers of the 192 allele. After 10 weeks of training, 1RM, MV, and MQ increased significantly for all groups combined (P < 0.001). However, carriers of the 192 allele gained significantly more strength with ST than non-carriers of the 192 allele (P = 0.02). There was also a non-significant trend for a greater increase in MV in 192 carriers than non-carriers (P = 0.08). No significant associations were observed for the other polymorphisms studied. Thus, these data suggest that the IGF1 promoter polymorphism may influence the strength response to ST. Larger sample sizes should be used in future studies to verify these results