Substrate utilization during exercise with glucose and glucose plus fructose ingestion in boys ages 10--14 yr.
We measured substrate utilization during exercise performed with water (W), exogenous glucose (G), and exogenous fructose plus glucose (FG) ingestion in boys age 10-14 yr. Subjects (n = 12) cycled for 90 min at 55% maximal O(2) uptake while ingesting either W (25 ml/kg), 6% G (1.5 g/kg), or 3% F plus 3% G (1.5 g/kg). Fat oxidation increased during exercise in all trials but was higher in the W (0.28 +/- 0.023 g/min) than in the G (0.24 +/- 0.023 g/min) and FG (0.25 +/- 0.029 g/min) trials (P = 0.04). Conversely, total carbohydrate (CHO) oxidation decreased in all trials and was lower in the W (0.63 +/- 0.05 g/min) than in the G (0.78 +/- 0.051 g/min) and FG (0.74 +/- 0.056 g/min) trials (P = 0.009). Exogenous CHO oxidation, as determined by expired (13)CO(2), reached a maximum of 0.36 +/- 0.032 and 0.31 +/- 0.030 g/min at 90 min in G and FG, respectively (P = 0.04). Plasma insulin levels decrease during exercise in all trials but were twofold higher in G than in W and FG (P < 0.001). Plasma glucose levels decreased transiently after the onset of exercise in all trials and then returned to preexercise values in the W and FG (approximately 4.5 mmol/l) trials but were elevated by approximately 1.0 mmol/l in the G trial (P < 0.001). Plasma lactate concentrations decreased after the onset of exercise in all trials but were lower by approximately 0.5 mmol/l in W than in G and FG (P = 0.02). Thus, in boys exercising at a moderate intensity, the oxidation rate of G plus F is slightly less than G alone, but both spare endogenous CHO and fat to a similar extent. In addition, compared with flavored W, the ingestion of G alone and of G plus F delays exhaustion at 90% peak power by approximately 25 and 40%, respectively, after 90 min of moderate-intensity exercise.
Riddell
M C
MC
Children's Exercise and Nutrition Centre, McMaster University, Hamilton, Ontario, Canada L8N 3Z5.
Bar-Or
O
O
Wilk
B
B
Parolin
M L
ML
Heigenhauser
G J
GJ
D000293:Adolescent; D001786:Blood Glucose / Q000378:metabolism; D001824:Body Constitution; D050260:Carbohydrate Metabolism; D002245:Carbon Dioxide / Q000032:analysis; D002247:Carbon Isotopes; D002648:Child; D004040:Dietary Carbohydrates; D015444:Exercise / Q000502:physiology*; D005632:Fructose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006339:Heart Rate; D006801:Humans; D007328:Insulin / Q000097:blood; D007773:Lactates / Q000097:blood; D016018:Least-Squares Analysis; D050356:Lipid Metabolism; D008297:Male; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012044:Regression Analysis
D001786:Blood Glucose; D002247:Carbon Isotopes; D004040:Dietary Carbohydrates; D007328:Insulin; D007773:Lactates; D002245:Carbon Dioxide; D005632:Fructose; D005947:Glucose