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Department of Physical Education, Odense University, DK-5230 Odense M; and Copenhagen Muscle Research Center, Rigshospitalet, August Krogh Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark
Received 14 May 1996; accepted in final form 13 August 1996.
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 · kg1
performed 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.
ammonia; glutamine; tryptophan; endurance exercise; well-trained athletes
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