Background: Exercise has several positive effects on glucose metabolism, however previous studies showed a higher blood glucose curve after different types of exercise compared to a healthy oral glucose tolerance. We aimed to examine the acute effect of two different training methods on oral glucose tolerance, metabolic flexibility (MF) and fuel utilization during an oral glucose tolerance test (OGTT) in an endurance-trained (ETG) and a not endurance-trained group (CON).
Methods:
16 participants were included. Three different conditions were used, a resting state (Rest), a moderate-intensity 3-hour (3-H) session and a high intensity interval session (HIIT) on an ergometer. The exercise sessions were done in the evening, followed by a muscle biopsy and blood sampling combined with an OGTT and resting metabolic rates (RMR) the morning after.
Results:
Only 3-H resulted in a significantly lower oral glucose tolerance in both groups compared to HIIT and Rest. No differences in MF were seen between the groups. Furthermore, exercise did not affect MF within either group. Higher levels of fat oxidation and plasma free fatty acids (FFA) levels combined with lower muscle glycogen content were detected after 3-H compared to Rest and HIIT in both groups. Blood ketone levels were only elevated after 3-H in the ETG.
Conclusion:
The present study shows that 3-hours on an ergometer lead to a reduced oral glucose tolerance, a higher fat oxidation and an inhibition of glucose uptake into the muscle cell proposedly through increased plasma FFA levels in endurance-trained and not endurance-trained healthy subjects. No differences in MF between the groups were detected and MF was not affected by the exercise sessions in either group. Therefore, from a health perspective, the duration of long moderate intensity exercises needs to be restricted to maintain a high glucose tolerance and avoid temporarily disturbed glucose control.