Strength training: importance of genetic factors

Purpose: This study focuses on the quantification of genetic and environmental factors in arm strength after high-resistance strength training. Methods: Male monozygolic (MZ, N = 2.5) and dizygotic (DZ, N = 16) twins (22.4 +/- 3.7 yr) participated in a IO-wk resistance training program for the elbow flexors. The evidence for genotype*training interaction, or association of interinidividual differences in training effects with the genotype, was tested by a two-way ANOVA in the MZ twins and using a bivariate model-fitting approach on pre-and post-training phenotypes in MZ and DZ twins. One repetition maximum (1RM), isometric strength, and concentric and eccentric moments in 110 degrees arm flexion at velocities of 30 degrees.s(-1), 60 degrees.s(-1), and 120 degrees.s(-1) were evaluated as well as arm muscle cross-sectional area (MCSA). Results: Results indicated significant positive training effects for all measures except for maximal eccentric moments. Evidence for genotype*training interaction was found for 1RM I and isometric strength, with MZ intra-pair correlations of 0.46 and 0.30, respectively. Bivariate model-fitting indicated that about 20% of the variation in post-training 1RM isometric strength, and concentric moment at 120 degrees.s(-1) was explained by training-specific genetic factors that were independent from genetic factors that explained variation in the pretraining phenotype (30-77%). Conclusions: Genetic correlations between measures of pre-and post-training strength were indicative for high pleiotropic gene action and minor activation of training-specific genes during training.