It is thought that resistance exercise results in an increased need for
dietary protein; however, data also exists to support the opposite conclusion. The purpose of this study was to determine the impact of resistance exercise training on
protein metabolism in novices with the hypothesis that
resistance training would reduce
protein turnover and improve whole-body
protein retention. Healthy males (n = 8, 22 +/- 1 y, BMI = 25.3 +/- 1.8 kg.m(-2)) participated in a progressive whole-body split routine
resistance-training program 5d/week for 12 weeks. Before (PRE) and after (POST) the training, oral [15N]-
glycine ingestion was used to assess
nitrogen flux (Q),
protein synthesis (PS),
protein breakdown (PB), and net
protein balance (
NPB = PS-PB). Macronutrient intake was controlled over a 5d period PRE and POST, while estimates of
protein turnover and urinary
nitrogen balance (N(bal) = N(in) - urine N(out)) were conducted. Bench press and leg press increased 40% and 50%, respectively (p < 0.01). Fat- and bone-free mass (i.e., lean muscle mass) increased from PRE to POST (2.5 +/- 0.8 kg, p < 0.05). Significant PRE to POST decreases (p <0.05) occurred in Q (0.9 +/- 0.1 vs. 0.6 +/- 0.1 g N.kg(-1).d(-1)), PS (4.6 +/- 0.7 vs. 2.9 +/- 0.3 g.kg(-1).d(-1)), and PB (4.3 +/- 0.7 vs. 2.4 +/- 0.2 g.kg(-1).d(-1)). Significant training-induced increases in both
NPB (PRE = 0.22 +/- 0.13 g.kg(-1).d(-1); POST = 0.54 +/- 0.08 g.kg(-1).d(-1)) and urinary
nitrogen balance (PRE = 2.8 +/- 1.7 g N.d(-1); POST = 6.5 +/- 0.9 g N.d(-1)) were observed. A program of
resistance training that induced significant muscle
hypertrophy resulted in reductions of both whole-body PS and PB, but an improved
NPB, which favoured the accretion of skeletal muscle
protein. Urinary
nitrogen balance increased after training. The reduction in PS and PB and a higher
NPB in combination with an increased
nitrogen balance after training suggest that dietary requirements for
protein in novice resistance-trained athletes are not higher, but lower, after
resistance training.