Effects of glucose, glucose plus branched-chain amino acids, or placebo on bike performance over 100 km

Abstract

Madsen, Klavs, Dave A. MacLean, Bente Kiens, and Dirk Christensen. Effects of glucose, glucose plus branched-chain amino acids, or placebo on bike performance over 100 km. J. Appl. Physiol. 81(6): 2644–2650, 1996.—This study was undertaken to determine the effects of ingesting either glucose ( trial G) or glucose plus branched-chain amino acids (BCAA; trial B), compared with placebo ( trial P), during prolonged exercise. Nine well-trained cyclists with a maximal oxygen uptake of 63.1 ± 1.5 ml O2 ⋅ min−1 ⋅ kg−1performed three laboratory trials consisting of 100 km of cycling separated by 7 days between each trial. During these trials, the subjects were encouraged to complete the 100 km as fast as possible on their own bicycles connected to a magnetic brake. No differences in performance times were observed between the three trials (160.1 ± 4.1, 157.2 ± 4.5, and 159.8 ± 3.7 min, respectively). In trial B, plasma BCAA levels increased from 339 ± 28 μM at rest to 1,026 ± 62 μM after exercise ( P < 0.01). Plasma ammonia concentrations increased during the entire exercise period for all three trials and were significantly higher in trial B compared with trials G and P ( P< 0.05). The respiratory exchange ratio was similar in the three trials during the first 90 min of exercise; thereafter, it tended to drop more in trial P than in trials G and B. These data suggest that neither glucose nor glucose plus BCAA ingestion during 100 km of cycling enhance performance in well-trained cyclists.