Six endurance-trained men [peak oxygen uptake (Vo2) = 4.58 ± 0.50 (SE) l/mini completed 60 min of exercise at a workload requiring 68 ± 2% peak Vo2 in an environmental chamber maintained at 35°C (<50% relative humidity) on two occasions, separated by at least I wk. Subjects ingested either a 6% glucose solution containing 1 μCi [3-3H]glucose/g glucose (CHO trial) or a sweet placebo (Con trial) during the trials. Rates of hepatic glucose production [HGP = glucose rate of appearance (Ra) in Con trial] and glucose disappearance (Rd), were measured using a primed, continuous infusion of [6,6-2H]glucose, corrected for gut-derived glucose (gut Ra) in the CHO trial. No differences in heart rate, Vo2, respiratory exchange ratio, or rectal temperature were observed between trials, Plasma glucose concentrations were similar at rest but increased (P < 0.05) to a greater extent in the CHO trial compared with the Con trial. This was due to the absorption of ingested glucose in the CHO trial, because gut Ra after 30 and 50 min (16 ± 5 μmol·kg-1·min-1) was higher (P < 0.05) compared with rest, whereas HGP during exercise was not different between trials. Glucose Rd was higher (P < 0.05) in the CHO trial after 30 and 50 min (48.0 ± 6.3 vs 34.6 ± 3.8 μmol·kg-1·min-1, CHO vs. Con, respectively). These results indicate that ingestion of carbohydrate, at a rate of ∼1.0 g/min, increases glucose Rd but does not blunt the rise in HGP during exercise in the heat.
|Number of pages||5|
|Journal||Journal of Applied Physiology|
|Publication status||Published - 15 Feb 2001|
- Heat stress
- Liver glucose output
- Muscle glucose uptake