Exercise capacity in subjects with type 1 diabetes mellitus in eu- and hyperglycaemia

Circumstantial evidence suggests that an increase in plasma glucose availability improves exercise capacity in subjects with type 1 diabetes mellitus. The aim of this study was to assess exercise capacity in eu- and hyperglycaemic conditions in subjects with type 1 diabetes.

Eight moderately exercise-trained male subjects with type 1 diabetes on continuous subcutaneous insulin infusion were studied. Using identical insulin infusion rates, the patients were randomly allocated to perform two stepwise ergometer tests in eu- and hyperglycaemic clamp conditions. The primary endpoint was the peak power output; the secondary endpoints comprised the rate of perceived exertion, lactate levels, heart rate, and respiratory exchange ratio.

Eu- and hyperglycaemic clamp conditions were observed at a plasma glucose concentration of 5.3 +/- 0.6 mmol/L and 12.4 +/- 2.1 mmol/L, respectively (mean +/- SD), and remained stable throughout the physical exercise. Insulin levels were similar in both conditions. Hyperglycaemia did not result in a significant increase in the peak power output compared to euglycaemia (mean paired difference of 4.96 W, 95% CI - 11.3 to 21.2, p = 0.49). Hyperglycaemia did not have a significant impact on the secondary endpoints compared to euglycaemia. Sensitivity analyses confirmed these results.

In subjects with type 1 diabetes, exercise capacity is not influenced by hyperglycaemia. Comparable levels of lactate and similar respiratory exchange ratio suggest that an increase in extracellular glucose availability did not translate into increased intracellular glucose oxidation.