Pre-exercise carbohydrate feeding may result in rebound hypoglycemia in some but not all athletes. The aim of the present study was to examine whether insulin sensitivity in athletes who develop rebound hypoglycemia is higher compared with those who do not show rebound hypoglycemia. Twenty trained athletes (VO(2max) of 61.8 +/- 1.4 ml.kg(-1).min(-1)) performed an exercise trial on a cycle ergometer. Forty-five minutes before the start of exercise, subjects consumed 500 ml of a beverage containing 75 g of glucose. The exercise trial consisted of 20 min of submaximal exercise at 74 +/- 1% VO(2max) immediately followed by a time trial. Based upon the plasma glucose nadir reached during submaximal exercise, subjects were assigned to a Hypo group (<3.5 mmol/L) and a Non-hypo group (> or =3.5 mmol/L). An oral glucose tolerance test was performed to obtain an index of insulin sensitivity (ISI). The plasma glucose nadir during submaximal exercise was significantly lower (p <.01) in the Hypo-group (n = 10) compared with the Non-hypo group (n = 10) (2.7 +/- 0.1 vs. 4.1 +/- 0.2 mmol/L, respectively). No difference was found in ISI between the Hypo and the Non-hypo group (3.7+/-0.4 vs. 3.8 +/- 0.5, respectively). The present results suggest that insulin sensitivity does not play an important role in the occurrence of rebound hypoglycemia.