Effect of carbohydrate intake during warming-up on the regulation of blood glucose during exercise

It has been shown that the intake of carbohydrate (CHO)-containing beverages under resting conditions may lead to a rebound hypoglycemia and decreased performance when exercise is performed thereafter. The aim of the present investigation was to study the effect of CHO beverage consumption with different CHO sources and different concentrations, during warming-up under practice-like circumstances, on the regulation of blood glucose during exercise. Eighteen highly trained cyclists consumed a standardized breakfast at 8:00 AM and performed a warming-up procedure at 10:00 AM for 20 min. Warming-up was followed by a 7-min break after which the subjects cycled for 45 min at a heart rate of 150. During warming-up a CHO-containing beverage (either sucrose, fructose, maltodextrin, or glucose) or a placebo was consumed in random order. The test was performed twice, with 300 ml and 600 ml intake, to study a possible dose-response effect. The results of the study showed that warming-up and final exercise lead to an increase of the catecholamines and a decrease of insulin. During the 7-min break this response was reversed. Glucose and maltodextrin induced the same insulin response. Increasing volume and higher CHO concentrations induced a longer increase in blood glucose level compared with the placebo intake. The results showed that intake of CHO-containing beverages during warming-up followed by a small break does not lead to rebound hypoglycemia, independent of the amount of CHO ingested, but instead increases blood glucose.