Abstract
During strenuous exercise (i.e. 70% maximal O2 consumption) there is a progressive shift from muscle glycogen to blood glucose oxidation
with increasing duration of exercise. By maintaining blood glucose concentration and
the rate of carbohydrate oxidation necessary to exercise strenuously, carbohydrate
consumption throughout exercise delays fatigue by 30-60 min in endurance-trained subjects.
This requires exogenous glucose supplementation at rates in excess of 1 gram/min (i.e.,
16 mg/kg/min) as evidenced by the observation that intravenous glucose infusion at
this rate is required to maintain blood glucose at 5 mM. Exogenous glucose must be
infused at a rate of 2.6 gram/min (i.e., 37 mg/kg/min), which is similar to the total
rate of carbohydrate oxidation, in order to maintain blood glucose at 10 mM after
2 h of exercise. However, carbohydrate supplementation during intense exercise does
not spare muscle glycogen utilization in people. This suggests that over the course
of 2-4 hours of exercise at 70% V̇O2max, muscle glycogen and blood glucose contribute equally to total carbohydrate oxidation.
Furthermore, during the latter stages of prolonged exercise, exogenous blood glucose
supplementation may be capable of supplying almost all of the carbohydrate requirements
of exercise at intensities up to 70% V̇O2max.
Key words
Blood glucose - glucose supplementation - endurance-trained qubjects
