Abstract
We evaluated the impact of protein supplementation on adaptations to arduous concurrent training in healthy adults with potential applications to individuals undergoing military training. Peer-reviewed papers published in English meeting the population, intervention, comparison and outcome criteria were included. Database searches were completed in PubMed, Web of science and SPORTDiscus. Study quality was evaluated using the COnsensus based standards for the selection of health status measurement instruments checklist. Of 11 studies included, nine focused on performance, six on body composition and four on muscle recovery. Cohen’s d effect sizes showed that protein supplementation improved performance outcomes in response to concurrent training (ES = 0.89, 95% CI = 0.08–1.70). When analysed separately, improvements in muscle strength (SMD = +4.92 kg, 95% CI = −2.70–12.54 kg) were found, but not in aerobic endurance. Gains in fat-free mass (SMD = +0.75 kg, 95% CI = 0.44–1.06 kg) and reductions in fat-mass (SMD = −0.99, 95% CI = −1.43–0.23 kg) were greater with protein supplementation. Most studies did not report protein turnover, nitrogen balance and/or total daily protein intake. Therefore, further research is warranted. However, our findings infer that protein supplementation may support lean-mass accretion and strength gains during arduous concurrent training in physical active populations, including military recruits.
Highlights
Concurrent training is defined as the combination of resistance and endurance training as part of a periodised physical training model [1]
This review identified 11 studies which investigated the effects of protein supplementation on exercise performance, body composition and muscle recovery adaptations to concurrent exercise training compared to a placebo in healthy adults, confirming the need for more work in this area
Including measures of protein metabolism, such as nitrogen balance and protein turnover, in future work should be considered as a means of better understanding the effects of protein supplementation during military recruit training. This is the first systematic review and meta-analysis to investigate the effects of protein supplementation on arduous concurrent training adaptations
Summary
Concurrent training is defined as the combination of resistance and endurance training as part of a periodised physical training model [1]. Chronic endurance training improves the oxidative capacity of muscle, which can increase whole-body oxygen uptake, leading to a more fatigue-resistant muscle, whereas resistance training develops muscle strength [21] Both modes of exercise have been shown to increase the phosphorylation of protein in the protein kinase B-mammalian target of rapamycin-p70 ribosomal protein S6 kinase (Akt-mTOR-p70S6K) pathway, leading to an increase of MPS [20]. Endurance exercise stimulates a rise in adenosine monophosphate-activated protein kinase (AMPK) [32], which may inhibit mTOR through the activation of the tuberous sclerosis complex (TSC) [2] This has the potential to reduce the post-exercise MPS response, and subsequently attenuate muscle strength adaptations [27] when individuals undertake concurrent endurance training [28]
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