Nutrition research (New York, N.Y.)Mar 25, 2014

Taking branched-chain amino acids and carbs before exercise does not boost muscle-building signals after resistance training in men

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Apr 1, 2026

Abstract

Significant increases in insulin and glucose levels were observed after carbohydrate (CHO) and carbohydrate plus branched-chain amino acid (BCAA) supplementation.

Resistance exercise (RE) was performed by 27 males who were divided into three groups: CHO, CHO + BCAA, and placebo (PLC).
Serum insulin and glucose levels showed significant increases in both CHO and CHO + BCAA groups compared to the PLC group.
Phosphorylated levels of muscle signaling markers, including insulin receptor substrate 1 (IRS-1), protein kinase B, and mammalian target of rapamycin, significantly increased over time.
Carbohydrate and CHO + BCAA supplementation significantly raised IRS-1 levels compared to the PLC group.
No additional benefits in muscle signaling markers indicative of protein synthesis were found with the coingestion of CHO and BCAA compared to CHO alone.

Simplified

The effects of a single bout of resistance exercise (RE) in conjunction with periexercise branched-chain amino acid (BCAA) and carbohydrate (CHO) ingestion on skeletal muscle signaling markers indicative of muscle protein synthesis were determined. It was hypothesized that CHO + BCAA would elicit a more profound effect on these signaling markers compared with CHO. Twenty-seven males were randomly assigned to CHO, CHO + BCAA, or placebo (PLC) groups. Four sets of leg presses and leg extensions were performed at 80% 1 repetition maximum. Supplements were ingested 30 minutes and immediately before and after RE. Venous blood and muscle biopsy samples were obtained immediately before supplement ingestion and 0.5, 2, and 6 hours after RE. Serum insulin and glucose and phosphorylated levels of muscle insulin receptor substrate 1 (IRS-1), protein kinase B, mammalian target of rapamycin, phosphorylated 70S6 kinase, and 4E binding protein 1 were assessed. Data were analyzed by 2-way repeated-measures analysis of variance. Significant group × time interactions were observed for glucose and insulin (P < .05) showing that CHO and CHO + BCAA were significantly greater than PLC. Significant time main effects were observed for IRS-1 (P = .001), protein kinase B (P = .031), mammalian target of rapamycin (P = .003), and phosphorylated 70S6 kinase (P = .001). Carbohydrate and CHO + BCAA supplementation significantly increased IRS-1 compared with PLC (P = .002). However, periexercise coingestion of CHO and BCAA did not augment RE-induced increases in skeletal muscle signaling markers indicative of muscle protein synthesis when compared with CHO.

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Taking branched-chain amino acids and carbs before exercise does not boost muscle-building signals after resistance training in men

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