Branched-Chain Amino Acid Supplementation Enhances Substrate Metabolism, Exercise Efficiency and Reduces Post-Exercise Fatigue in Active Young Males

Abstract

Background: Branched-chain amino acids (BCAAs, isoleucine, leucine, and valine) are commonly applied to promote muscle protein synthesis. However, the effects of BCAAs on exercise-induced substrate metabolism, performance and post-exercise fatigue during endurance exercise remain unclear. Methods: In a double-blind cross-over design, eleven active males completed 1 h of constant load exercise (CLE) at 60% VO₂max power followed by a time to exhaustion (TTE) test at 80% VO₂max power after supplementation with BCAAs or placebo on consecutive three days. During exercise, indirect calorimetry was used to measure the carbohydrate (CHO) and fat oxidation rate, as well as the cycling efficiency. In addition, rating of perceived exertion (RPE) and visual analogue scale (VAS) scores were obtained at interval times during the whole period. Fingertips and venous blood (n = 8) were collected for the measurement of metabolic responses at different time points during exercise. Results: Compared to the placebo group, the fat oxidation rate was significantly higher after 20 and 30 min of CLE (p < 0.05). The CHO oxidation rates showed a significant increase in the BCAA group during TTE (p < 0.05). Meanwhile, the cycling efficiency during TTE was significantly improved (p < 0.05). Interestingly, VAS significantly decreased post-exercise in the BCAA group (p < 0.05). Additionally, the levels of blood insulin between the two groups were significantly higher in the post-exercise period compared to the pre-exercise periods (p < 0.001), while insulin levels were significantly lower in the post-exercise period with supplemental BCAAs compared to the placebo (p < 0.001). BCAAs also enhanced the levels of blood ammonia in the post-exercise period compared to the fasting and pre-exercise periods (BCAA: p < 0.01; Placebo: p < 0.001). However, in the post-exercise period, blood ammonia levels were significantly lower in the BCAA group than in the placebo group (p < 0.05). Conclusions: This study shows the critical role of BCAAs during exercise in active males and finds that BCAA supplementation enhanced fat oxidation during the CLE, increased carbohydrate oxidation and exercise efficiency during the TTE, and reduced immediate post-exercise fatigue.

Keywords: BCAA; CHO oxidation; exercise performance; fat oxidation; substrate metabolism.

Figure 1

The figure depicts the framework of the study. The experiments started after three days of BCAAs supplemented twice per day. The endurance exercise was subsequently monitored by testing parameters such as blood, respiration and heart rates. After the exercise, the parameters were tested again to evaluate them post-exercise.

Figure 2

Fat and carbohydrate oxidation during exercise after BCAA supplementation. Respiratory gases were collected to calculate the oxidation rates marked FATox (a,b) and CHOox (c,d), respectively. * p < 0.05, n = 11. (a): Fat oxidation rate at different times during CLE, (b): The area under the curve (AUC) of fat oxidation during CLE, (c): CHO oxidation rate at different times during CLE, (d): The AUC of CHO oxidation during CLE. BCAA: Branched-chain amino acids.

Figure 3

Blood glucose and lactate are not affected by BCAA supplements. The level of glucose (a,b) and lactate (c,d) during CLE and post-exercise. Values are means ± SD, n = 11. (a): Glucose level at different times, (b): Glucose AUC, (c): Lactate level at different times, (d): Lactate AUC. BCAA: Branched-chain amino acids.

Figure 4

Non-esterified fatty acid (NEFA) levels in serum at fasting, pre-exercise and post-exercise. n = 8. ^&&& p < 0.001, vs. Pre-ex; ^## p < 0.01, ^### p < 0.001, vs. fasting. Pre-ex: pre-exercise, Post-ex: post-exercise.

Figure 5

Blood insulin levels in serum at fasting, pre-exercise and post-exercise with BCAA supplements. n = 8. *** p < 0.001, ^&&& p < 0.001. Pre-ex: pre-exercise, Post-ex: post-exercise. INS: Insulin.

Figure 6

Time (a) and cycling efficiency (b) during TTE between two groups. n = 11. Values are means ± SD. * p < 0.05 vs. placebo group. TTE: time to exhaustion. BCAA: Branched-chain amino acids.

Figure 7

BCAA supplementation has no effect on heart activity during acute endurance exercise. (a) Heat rate (HR) was measured during 1 h of acute endurance exercise. (b) Rated perceived exertion (RPE) was detected at the same time. n = 11. Values are means ± SD.

Figure 8

BCAA supplementation relieves acute exercise-induced fatigue. (a) VAS was measured during CLE. (b) Blood ammonia levels were detected in serum during fasting, pre-exercise and post-exercise. In (a), n = 11; in (b): n = 8. Values are means ± SD. * p < 0.05, ^&& p < 0.01, ^&&& p < 0.001, ^### p < 0.001.

Figure 9

Conclusive figure. The figure shows an overview of the experiments.