Journal Title (Medline/Pubmed accepted abbreviation): J Strength Cond Res
Volume: Published ahead of print
Hypothesis: Branched-chain amino acid (BCAA) supplementation will enhance aerobic performance, ratings of perceived exertion (RPE), or substrate utilization compared with an isocaloric carbohydrate (CHO) beverage or a noncaloric placebo (PLAC) beverage.
Subjects: 9 healthy, untrained men participated in the study. Mean ± standard deviation subject characteristics evaluated included age (21.6 ± 3.2 years), weight (84.2 ± 17.0 kg), body mass index (BMI; 26.3 ± 4.3 kg/m2), and peak oxygen uptake (36.3 ± 2.2 mL/kg/min and 3.0 ± 0.5 L/min).
Experimental design: Randomized, blinded, repeated measures
Treatments and protocol: Baseline testing included assessment of body weight and peak oxygen consumption. Subjects maintained detailed dietary intake records for 3 days before and on the day of each exercise trial and were asked to avoid eating for 4 hours before each trial. Mean intake of several dietary factors (eg, energy, CHO, protein, fat, vitamin C, and vitamin E) were determined to verify that these components did not significantly differ between trials. The study included 3 treatment phases, which began at least 2 weeks after initial peak oxygen consumption testing. Eight weeks separated each trial. Subjects were discouraged from any strenuous physical activity throughout the course of the trials. During each exercise trial, after 15-minutes of seated rest and the 4-hour fast, a resting blood sample was drawn. Subjects were given a 5-minute warm-up on a Monark cycle ergometer at 50 revolutions per minute and a resistance of 1 kp. After the warm-up, resistance was increased to a workload eliciting an intensity of 55% peak oxygen consumption. Steady-state exercise continued for 90 minutes, during which time expired air was monitored throughout, and RPE and the respiratory exchange ratio (RER) were monitored every 15 minutes. After the steady-state ride, subjects completed a 15-minute time trial in which they covered as much distance as possible. The 3 treatment trials differed only in the beverage consumed (ie, BCAA, CHO, or PLAC). Subjects were assigned at random to each of 3 treatment orders to ensure that no trial had an advantage due to order effect. One serving of the BCAA beverage contained 4.800 g isoleucine, 12.2 g leucine, and 7.30 g valine (100 kcal). Beverages were administered 5 minutes before the initiation of exercise and at the 60-minute mark. The total amount of energy given to subjects over the 2 time points for the BCAA and CHO trials was 200 kcal. In addition to the pre-exercise sample, a blood sample was taken immediately after exercise to determine blood glucose and BCAA concentrations. Based on analysis of variance (ANOVA), the level of statistical analysis was set at P < .05.
The study demonstrates that BCAA supplementation reduces RPE after 1 hour of aerobic exercise, but does not improve performance compared with PLAC. Based on the study results, there would be neither deleterious nor beneficial performance effect to adding BCAA to a CHO beverage under conditions in which sufficient muscle glycogen is present. Many athletes use BCAA supplementation during aerobic training sessions, often in lieu of CHO ingestion. Because BCAA supplementation reduces certain indices of muscle damage, and because whole protein ingestion during an aerobic exercise session may benefit performance in a subsequent exercise session, the present study suggests that BCAA supplementation during aerobic exercise should be combined with a CHO-containing beverage.