Purpose: Endurance training enhances skeletal muscle glucose uptake at rest, but the responses to different exercise intensities are unknown. In the present study, we tested whether glucose uptake is enhanced in trained men during low-, moderate-, and high-intensity exercise as compared with untrained men.
Methods: Seven trained and untrained men were studied without any dietary manipulation during bicycle exercise at relative intensities of 30%, 55%, and 75% of maximal oxygen consumption ([OV0312]O(2max)) on three separate days. Glucose uptake in the quadriceps femoris muscle was directly measured using positron emission tomography (PET) and 18F-fluoro-deoxy-glucose ([18F]FDG). [18F]FDG was injected 10 min after the start of the exercise. Thereafter exercise was continued for another 25 min. PET scanning was conducted immediately after completion of the exercise. The measured glucose uptake values reflect the situation during exercise due to chemical characteristics of the [18F]FDG.
Results: Muscle glucose uptake increased from 30% to 55% [OV0312]O(2max) intensity exercise similarly in both groups (P < 0.05). However, from 55% to 75% [OV0312]O(2max) intensity exercise, only athletes were able to further enhance glucose uptake. Furthermore, at highest intensity, glucose uptake was significantly higher in trained than in untrained men (236.6 +/- 29.6 vs 176.3 +/- 22.4 micromol.kg-1.min-1, P < 0.05). There were no differences in plasma glucose, insulin, or lactate in any time point at 75% [OV0312]O(2max) intensity between groups.
Conclusions: These results show that skeletal muscle glucose uptake is higher in trained than in untrained men at high relative exercise intensity, although at lower relative exercise intensities no differences are observed. Thus, endurance training improves the capacity of contraction-induced glucose uptake in skeletal muscle.