Resistance training reduces whole-body protein turnover and improves net protein retention in untrained young males

Abstract

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 (Nbal = Nin – urine Nout) 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.