Retrospective Analysis Of Resistance Training-induced Strength And Hypertrophy: Separating The Wheat From The Hormone Chaff

Abstract

PURPOSE: To investigate associations between purportedly anabolic acute exercise-induced hormone responses and adaptations to resistance training in a cohort with normally distributed training-induced adaptations. METHODS: Acute post-exercise serum growth hormone (GH), free testosterone (fT), cortisol, and insulin-like growth factor (IGF-1) responses were determined at the midpoint of a 12-wk resistance exercise program conducted previously. Correlations of hormonal responses with gains in lean body mass (LBM), muscle fiber cross-sectional area (CSA) and leg press strength were investigated. Dietary factors were combined with hormonal responses as independent variables in multiple regression analysis of adaptations to resistance training. RESULTS: There were no significant correlations between the exercise-induced elevation (area under the curve_AUC) of GH, fT and IGF-1 and gains in LBM or leg press strength. Significant correlations were found for cortisol AUC with change in LBM (r = 0.29, P < 0.05) and type II fiber CSA (r = 0.35, P < 0.01) as well as GH AUC and gain in fiber area (type I: r=0.36, P=0.006; type II: r= 0.28, P=0.04). Multiple regression analysis showed that increments in daily dietary protein intake and the daily consumption of dairy, but no acute hormonal response, were significant predictors in a model of change in LBM and type II fiber area. CONCLUSION: A significant association existed between GH and cortisol and fiber hypertrophy, but there was no association between any hormones and strength gains. Multiple regression analysis revealed an important role of increasing dietary protein and servings of dairy in promoting training-induced gains in LBM and fiber hypertrophy. In contrast, post-exercise elevations in endogenous hormones were relatively impotent in their predictive value for resistance training-induced hypertrophy calling into question persistent referrals, which are frequently erroneously based on pharmacological intervention studies, to their anabolic capacity. Supported by NSERC and CIHR