Abstract
The ingestion of intact protein or essential amino acids (EAA) stimulates mechanistic target of rapamycin complex-1 (mTORC1) signaling and muscle protein synthesis (MPS) following resistance exercise. The purpose of this study was to investigate the response of myofibrillar-MPS to ingestion of branched-chain amino acids (BCAAs) only (i.e., without concurrent ingestion of other EAA, intact protein, or other macronutrients) following resistance exercise in humans. Ten young (20.1 ± 1.3 years), resistance-trained men completed two trials, ingesting either 5.6 g BCAA or a placebo (PLA) drink immediately after resistance exercise. Myofibrillar-MPS was measured during exercise recovery with a primed, constant infusion of L-[ring13C6] phenylalanine and collection of muscle biopsies pre and 4 h-post drink ingestion. Blood samples were collected at time-points before and after drink ingestion. Western blotting was used to measure the phosphorylation status of mTORC1 signaling proteins in biopsies collected pre, 1-, and 4 h-post drink. The percentage increase from baseline in plasma leucine (300 ± 96%), isoleucine (300 ± 88%), and valine (144 ± 59%) concentrations peaked 0.5 h-post drink in BCAA. A greater phosphorylation status of S6K1Thr389 (P = 0.017) and PRAS40 (P = 0.037) was observed in BCAA than PLA at 1 h-post drink ingestion. Myofibrillar-MPS was 22% higher (P = 0.012) in BCAA (0.110 ± 0.009%/h) than PLA (0.090 ± 0.006%/h). Phenylalanine Ra was ~6% lower in BCAA (18.00 ± 4.31 μmol·kgBM−1) than PLA (21.75 ± 4.89 μmol·kgBM−1; P = 0.028) after drink ingestion. We conclude that ingesting BCAAs alone increases the post-exercise stimulation of myofibrillar-MPS and phosphorylation status mTORC1 signaling.
Highlights
It is well-established that ingestion of essential amino acids (EAA) following resistance exercise stimulates an increased response of muscle protein synthesis MPS in humans (Smith et al, 1998; Tipton et al, 1999a)
The present study demonstrated that ingesting of all three branched-chain amino acids (BCAAs) alone, without concurrent ingestion of other EAA, protein, or macronutrients, stimulated a 22% greater response of myofibrillar-MPS following resistance exercise compared with a placebo
The magnitude of this increased response of myofibrillar-MPS was ∼50% less than the previously reported myofibrillar-MPS response to a dose of whey protein containing similar amounts of BCAAs (Churchward-Venne et al, 2012; Witard et al, 2014). These results demonstrate that BCAAs exhibit the capacity to stimulate myofibrillar-MPS, a full complement of EAA could be necessary to stimulate a maximal response of myofibrillar-MPS following resistance exercise
Summary
It is well-established that ingestion of essential amino acids (EAA) following resistance exercise stimulates an increased response of muscle protein synthesis MPS in humans (Smith et al, 1998; Tipton et al, 1999a). More recent evidence from studies in rodents and cell culture models suggest that the stimulation of MPS by EAA may be mediated by a few amino acids rather than a combination of all EAA (Crozier et al, 2005; Kimball and Jefferson, 2006). The response of MPS to leucine provision has been extensively investigated over the past two decades, both in cell culture studies (Buse and Reid, 1975; Kimball and Jefferson, 2006; Atherton et al, 2010b) and in vivo rodent (Anthony et al, 1999, 2000; Crozier et al, 2005; Norton et al, 2012) and human (Matthews, 2005; Wilkinson et al, 2013) studies
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