Summary
The availability of carbohydrate (CHO) as a substrate for the exercising muscles is known to be a limiting factor in the performance of prolonged cycle exercise, and provision of exogenous CHO in the form of glucose can increase endurance capacity. The present study examined the effects of ingestion of fluids and of CHO in different forms on exercise performance. Six male volunteers exercised to exhaustion on a cycle ergometer at a workload which required approximately 70% of\(\dot V_{O_2 \max }\). After one preliminary trial, subjects performed this exercise test on six occasions, one week apart. Immediately before exercise, and at 10-min intervals throughout, subjects ingested 100 ml of one of the following: control (no drink), water, glucose syrup, fructose syrup, glucose-fructose syrup or a dilute glucose-electrolyte solution. Each of the syrup solutions contained approximately 36 g CHO per 100 ml; the isotonic glucose-electrolyte solution contained 4 g glucose per 100 ml. A randomised Latin square order of administration of trials was employed. Expired air samples for determination of\(\dot V_{O_2 }\), respiratory exchange ratio and rate of CHO oxidation were collected at 15-min intervals. Venous blood samples were obtained before and after exercise. Subjects drinking the isotonic glucose-electrolyte solution exercised longer (90.8 (12.4) min, mean (SEM)) than on the control test (70.2 (8.3) min; p<0.05). Endurance capacity was not affected by any of the other drinks. Blood glucose concentration at exhaustion was higher when concentrated sugar solutions were given, but no instance of hyperglycaemia or hypoglycaemia was observed in any trial. Neither the rate of CHO oxidation nor the total amount of CHO oxidised was influenced by the ingestion of large quantities of glucose or fructose.
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Maughan, R.J., Fenn, C.E. & Leiper, J.B. Effects of fluid, electrolyte and substrate ingestion on endurance capacity. Europ. J. Appl. Physiol. 58, 481–486 (1989). https://doi.org/10.1007/BF02330701
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DOI: https://doi.org/10.1007/BF02330701