Effects of 4 h preexercise carbohydrate feedings on cycling performance.
This study determined the effects of consuming three different amounts of liquid carbohydrate 4 h before exercise on the metabolic responses during exercise and on exercise performance. Four hours before exercise subjects consumed either 45 (L) or 156 (M) g of carbohydrate in isocaloric feedings and either 0 (P) or 312 (H) g of carbohydrate. Interval cycling was undertaken for 95 min, followed by a performance trial. Blood glucose had reached basal 1 h after all feedings; blood insulin had reached basal 3 h after ingestion of P, L, and M but was still 84% higher for H at the start of exercise. During exercise insulin averaged 48% higher for H than P. Blood glucose decreased 16% during exercise for P, L, and M, whereas for H there was a transient drop the first 15 min of exercise, after which glucose increased and remained constant throughout exercise. More carbohydrate oxidation occurred during exercise for H vs P, whereas results were similar for L and M. Ingestion of H improved performance by 15% as compared with P, whereas performance was similar for L and M. These results indicate that, despite elevated insulin at the start of and during exercise, consumption of 312 g of carbohydrate 4 h before moderately intense prolonged exercise can improve performance, perhaps via an enhancement of carbohydrate oxidation.
Sherman
W M
WM
Exercise Physiology Laboratory, School of Health, Physical Education and Recreation, Ohio State University, Columbus 43210.
Brodowicz
G
G
Wright
D A
DA
Allen
W K
WK
Simonsen
J
J
Dernbach
A
A
D000328:Adult; D001642:Bicycling; D001786:Blood Glucose / Q000378:metabolism*; D001831:Body Temperature; D002986:Clinical Trials as Topic; D004040:Dietary Carbohydrates / Q000008:administration & dosage* / Q000097:blood; D015444:Exercise / Q000502:physiology; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D005990:Glycerol / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D008297:Male; D010101:Oxygen Consumption; D012007:Rectum; D013997:Time Factors
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D007773:Lactates; D019344:Lactic Acid; D005990:Glycerol