Effects of dietary manipulations on blood glucose and hormonal responses following supramaximal exercise

The effects of supramaximal exercise on blood glucose, insulin, and catecholamine responses were examined in 7 healthy male physical education students (mean±SD: age=21±1.2 years;\(\dot V_{{\text{O}}_{{\text{2 max}}} } \)=54±6 ml · kg⁻¹ · min⁻¹) in response to the following three dietary conditions: 1) a normal mixed diet (N); 2) a 24-h low carbohydrate (CHO) diet intended to reduce liver glycogen content (D₁); and 3) a 24-h low CHO diet preceded by a leg muscle CHO overloading protocol intended to reduce hepatic glycogen content with increased muscle glycogen store (D₂). Exercise was performed on a bicycle ergometer at an exercise intensity of 130%\(\dot V_{{\text{O}}_{{\text{2 max}}} } \) for 90 s. Irrespective of the dietary manipulation, supramaximal exercise was associated with a similar significant (p<0.01) increase in the exercise and recovery plasma glucose values. The increase in blood glucose levels was accompanied by a similar increase in insulin concentrations in all three groups despite lower resting insulin levels in conditions D₁ and D₂. Lactate concentrations were higher during the early phase of the recovery period in the D₂ as compared to the N condition. At cessation of exercise, epinephrine and norepinephrine were greatly elevated in all three conditions. These results indicate that the increase in plasma glucose and insulin associated with very high intensity exercise, persists in spite of dietary manipulations intended to reduce liver glycogen content or increase muscle glycogen store. These data suggest that the blood glucose increase following supramaximal exercise is most likely related to hepatic glycogenolysis in spite of a substantial decrease in liver glycogen content.