Essential amino acid and carbohydrate ingestion before resistance exercise does not enhance postexercise muscle protein synthesis

Abstract

Ingestion of an essential amino acid-carbohydrate (EAA + CHO) solution following resistance exercise enhances muscle protein synthesis during postexercise recovery. It is unclear whether EAA + CHO ingestion before resistance exercise can improve direct measures of postexercise muscle protein synthesis (fractional synthetic rate; FSR). We hypothesized that EAA + CHO ingestion before a bout of resistance exercise would prevent the exercise-induced decrease in muscle FSR and would result in an enhanced rate of muscle FSR during postexercise recovery. We studied 22 young healthy subjects before, during, and for 2 h following a bout of high-intensity leg resistance exercise. The fasting control group (n = 11) did not ingest nutrients, and the EAA + CHO group (n = 11) ingested a solution of EAA + CHO 1 h before beginning the exercise bout. Stable isotopic methods were used in combination with muscle biopsies to determine FSR. Immunoblotting procedures were utilized to assess cell signaling proteins associated with the regulation of FSR. We found that muscle FSR increased in the EAA + CHO group immediately following EAA + CHO ingestion (P < 0.05), returned to basal values during exercise, and remained unchanged at 1 h postexercise. Muscle FSR decreased in the fasting group during exercise and increased at 1 h postexercise (P < 0.05). However, the 2 h postexercise FSR increased by approximately 50% in both groups with no differences between groups (P > 0.05). Eukaryotic elongation factor 2 phosphorylation was reduced in both groups at 2 h postexercise (EAA + CHO: 39 +/- 7%; fasting: 47 +/- 9%; P < 0.05). We conclude that EAA + CHO ingestion before resistance exercise does not enhance postexercise FSR compared with exercise without nutrients.

Figures

Fig. 1.

Study design. Blood and muscle sampling are indicated by arrows. A detailed description of the study design is provided in the text. Study design was identical for the fasting control group and the leucine-enriched essential amino acid and carbohydrate (EAA + CHO) group except for the ingestion of nutrients (+/−).

Fig. 2.

A: muscle protein fractional synthetic rate (FSR) time course in both the fasting control group and the EAA + CHO group. FSR was determined during a preexercise period (Pre-Ex), during exercise (Ex), 1 h postexercise (1 h Post-Ex), and 2 h postexercise (2 h Post-Ex). Nutrients were ingested immediately following the first muscle biopsy in the EAA + CHO group during the Pre-Ex period. B: FSR in both the fasting control and EAA + CHO groups over the entire 2 h postexercise recovery period (i.e., rate of incorporation calculated from the biopsy collected immediately postexercise to the biopsy collected at 2 h postexercise). Fasting control group data have been previously published (9). Values are means ± SE. *P < 0.05 vs. fasting Pre-Ex. # P < 0.05 vs. fasting at respective time point.

Fig. 3.

Time course of blood phenylalanine concentration (A) and net balance (B) across the leg in the preexercise state (Pre-Ex), during exercise (Ex), 1 h postexercise (1 h Post-Ex), and 2 h postexercise (2 h Post-Ex) for both the fasting control and EAA + CHO groups. Data shown are presented as the hourly average. Pre-Ex data for the fasting group are basal data without nutrients, whereas Pre-Ex data for the EAA + CHO are the hourly average following nutrient ingestion. Values are means ± SE. # P < 0.05 vs. fasting at respective time point.

Fig. 4.

Upstream regulators of the mammalian target of rapamycin (mTOR) signaling pathway in the EAA + CHO and fasting control group 1 h before exercise (1 h Pre-Ex), immediately before beginning exercise (Pre-Ex), immediately following exercise (Post-Ex), 1 h postexercise (1 h Post-Ex), and 2 h postexercise (2 h Post-Ex) . Nutrients were ingested immediately following the first muscle biopsy (1 h Pre-Ex) in the EAA + CHO group. A: Akt/protein kinase B (PKB) phosphorylation at Ser473. B: AMP-activated protein kinase (AMPKα2) activity. The time course data for the fasting control group have been previously published (9). Values are means ± SE. *P < 0.05 vs. 1 h Pre-Ex. # P < 0.05 vs. fasting at respective time point. †P < 0.05 for time effect. There were no differences between groups for the AMPK data.

Fig. 5.

Phosphorylation status of downstream components of mTOR signaling pathway in the EAA + CHO and fasting control group 1 h before exercise (1 h Pre-Ex), immediately before beginning exercise (Pre-Ex), immediately following exercise (Post-Ex), 1 h postexercise (1 h Post-Ex), and 2 h postexercise (2 h Post-Ex). mTOR phosphorylation at Ser2448 (A), 4E-binding protein 1 (4E-BP1) phosphorylation at Thr37/46 (B), S6 kinase 1 (S6K1) phosphorylation at Thr389 (C), and eukaryotic elongation factor 2 (eEF2) phosphorylation at Thr56 (D) are shown. The time course phosphorylation data for the fasting group have been previously published (9). Values are means ± SE. *P < 0.05 vs. 1 h Pre-Ex. #P < 0.05 vs. fasting at respective time point.