Exogenous glucose oxidation during exercise in endurance-trained and untrained subjects.
To investigate the effect of training status on the fuel mixture used during exercise with glucose ingestion, seven endurance-trained cyclists (Tr; maximum O2 uptake 67 +/- 2.3 ml.kg-1.min-1) and eight untrained subjects (UTr; 48 +/- 2 ml.kg-1.min-1) were studied during 120 min of exercise at approximately 60% maximum O2 uptake. At the onset of exercise, 8 ml.kg-1.min-1 of an 8% naturally enriched [13C]glucose solution was ingested and 2 ml/kg every 15 min thereafter. Energy expenditure was higher in Tr subjects compared with UTr subjects (3,404 vs. 2,630 kJ; P < 0.01). During the second hour, fat oxidation was higher in Tr subjects (37 +/- 2 g) compared with UTr subjects (23 +/- 1 g), whereas carbohydrate oxidation was similar (116 +/- 8 g in Tr subjects vs. 114 +/- 4 g in UTr subjects). No differences were observed in exogenous glucose oxidation (50 +/- 2 g in Tr subjects and 45 +/- 3 g in UTr subjects, respectively). Peak exogenous glucose oxidation rates were similar in the two groups (0.95 +/- 0.07 g/min in Tr subjects and 0.96 +/- 0.03 g/min in UTr subjects). It is concluded that the higher energy expenditure in Tr subjects during exercise at the same relative exercise intensity is entirely met by a higher rate of fat oxidation without changes in the rates of exogenous and endogenous carbohydrates.
Jeukendrup
A E
AE
Department of Human Biology, Maastricht University, The Netherlands. A.Jeukendrup@HB.UNIMAAS.NL
Mensink
M
M
Saris
W H
WH
Wagenmakers
A J
AJ
D000328:Adult; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D008297:Male
D005947:Glucose