The effect of glucose infusion on glucose kinetics during a 1-h time trial.
OBJECTIVE
To investigate the effect of glucose infusion on glucose kinetics and performance, six endurance cyclists (VO2max = 61.7 +/- 2.0 (mean +/- SE) mL x kg(-1) x min(-1)) completed two performance trials in which they had to accomplish a set amount of work as quickly as possible (991 +/- 41 kJ). Subjects were infused with either glucose (20% in saline; carbohydrate (CHO)) at a rate of 1 g x min(-1) or saline (0.9% saline; placebo (PLA)). It was hypothesized that time trial performance would be unaffected by the infusion of glucose, as endogenous stores of CHO would not be limiting in the PLA trial.


RESULTS
Plasma glucose concentration increased from 4.8 +/- 0.1 mmol x L(-1) to 5.9 +/- 0.3 mmol x L(-1) during the PLA trial and from 4.9 +/- 0.1 mmol x L(-1) at rest to 12.4 +/- 1.1 mmol x L(-1) during the CHO trial. These values were significantly higher at all time points during the CHO trial compared with PLA (P < 0.001). In the final stages of the time trial, Rd in the PLA trial was 49 +/- 5 micromol x kg(-1) x min(-1) compared with 88 +/- 7 micromol x kg(-1) x min(-1) in the CHO trial (P < 0.05). Despite these differences, there was no difference in performance time between PLA and CHO (60.04 +/- 1.47 min, PLA, vs 59.90 +/- 1.49 min, CHO, respectively). Infused carbohydrate oxidation in the last 25% of the CHO trial was at least 675 +/- 120 micromol x kg(-1) and contributed 17 +/- 4% to total carbohydrate oxidation.


CONCLUSIONS
The results demonstrate that glucose infusion had no effect on 1-h cycle time-trial performance, despite an increased availability of plasma glucose for oxidation and evidence of increased glucose uptake into the tissues.
Carter
James M
JM
Human Performance Laboratory, School of Sport and Exercise Sciences, The University of Birmingham, Edgbaston, Birmingham, United Kingdom.
Jeukendrup
Asker E
AE
Mann
Chris H
CH
Jones
David A
DA
D000328:Adult; D001642:Bicycling; D001784:Blood Gas Analysis; D001786:Blood Glucose / Q000378:metabolism*; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D005947:Glucose / Q000008:administration & dosage*; D006339:Heart Rate; D006801:Humans; D008297:Male; D010084:Oxidation-Reduction; D013647:Task Performance and Analysis; D006113:United Kingdom
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005947:Glucose