EFFECT OF INFUSING BRANCHED-CHAIN AMINO-ACID DURING INCREMENTAL EXERCISE WITH REDUCED MUSCLE GLYCOGEN-CONTENT

The aim of this study was to investigate whether, when muscle glycogen is reduced, a pre-exercise infusion of branched-chain amino acids (BC AA) modifies exercise performance or the metabolic and respiratory res ponses to incremental exercise. Six moderately trained volunteers took part in the following protocol on two occasions. On day 1, at 9 a.m. in the postabsorptive state, they performed a graded incremental exerc ise (increases of 35 W every 4 min) to exhaustion (Ex-1). A meal of 1, 000 kcal (4,200 kJ; 60% protein, 40% fat) was consumed at 12 p.m. No f ood was then allowed until the end of the experiment (20-21 h later). A 90-min period of exercise at alternating high and moderate intensiti es, designed to deplete muscle glycogen, was performed between 6 p.m. and 7.30 p.m. The morning after (day 2), the subjects randomly receive d either a mixed solution of BCAA (260 mg x kg(-1) x h(-1) for 70 min) , or saline. They then repeated the graded incremental exercise to exh austion (Ex-2). Metabolic and respiratory measurements suggested a mus cle glycogen-depleted state had been achieved. No significant differen ces were observed in total work performed, maximal oxygen uptake or pl asma ammonia, alanine, and blood pyruvate concentrations in the two tr eatments. After BCAA infusion, higher blood lactate concentrations wer e observed at maximal power output in comparison with those during sal ine [BCAA 4.97 (SEM 0.41) mmol x 1(-1), Saline 3.88 (SEM 0.47) mmol x 1(-1), P < 0.05]. In summary, in conditions of reduced muscle glycogen content, after a short period of fasting, BCAA infusion had no signif icant effect on the total work that could be performed during a graded incremental exercise.