Resistance training and protein intake: muscular mass and volume variations in amateur bodybuilders

Background: Optimal nutrition, especially in terms of protein ingestion, is a tool to enhance the hypertrophic response to resistance training. The ingestion of high amounts of dietary protein in conjunction with resistance training reduces the rate of muscle protein breakdown when muscular hypertrophy of optimal restitution is the goal. Research question: The purpose of this study was to determine if and how protein intake increases muscular mass and volume after a six-month resistance training period in amateurs. Type of study: Longitudinal 'one-within, one-between' study. Methods: The sample group consisted of 13 amateur bodybuilders. The control group consisted of 36 amateur bodybuilders of the same age. Participants followed a controlled specific exercise protocol 3 times/week, using 3 sets of 8-6-4 Maximal Repetitions (MR). Subjects were interviewed about their usual diet to determine their daily protein intake, i.e. 2.03 ± 0.62 and 1.04 ± 0.05g/kg BW, in the experimental and control groups respectively. Anthropometric characteristics (body weight, body girth and skin-folds) were measured. A statistical analysis for longitudinal data was carried out using a random intercept model. Results: No statistical evidence of dietary regimen influence in muscle increase or statistically significant interaction between time and diet were found. The statistically significant changes detected in some muscles (i.e. chest girth p<0.05) come down from time trends, supporting the authors' hypothesis that they had only a training effect on the solicited body segments. Conclusions: This study's data analysis does not justify the excessive protein intake in amateur bodybuilders' diets aimed at increasing muscular mass and volume.