Effect Of Post-exercise Environmental Temperature On Glycogen Resynthesis

Abstract

Muscle glycogen can be a limiting factor in high-intensity and long-duration physical work. While many feeding strategies have investigated factors mediating synthesis, recovery temperature has not been previously studied. PURPOSE: To determine the effects of a hot (H) and room temperature (RT) environment on glycogen resynthesis during recovery from exercise. METHODS: Recreationally active males (n = 9) completed two 60-min cycling exercise sessions at 60% of maximum watts in a temperature controlled chamber (32.6°C), followed by 4 hours of recovery at the same temperature (H) or 22.2°C (RT). Subjects were fed a liquid dextrose solution (1.8 g/kg bodyweight) at 0 and 2 hours post-exercise. Muscle biopsies were taken from the vastus lateralis at 0, 2, and 4 hours post-exercise for the analysis of muscle glycogen. Blood samples were collected at 0, 30, 60, 120, 150, 180, and 240 minutes of recovery for blood glucose analysis. Ambient and core temperatures were recorded at 1-minute intervals for the duration of the trial. Expired gas was collected prior to 2- and 4-hour biopsies for calculation of whole body substrate oxidation. Glycogen, core temperature, and blood marker values were analyzed using two-way ANOVA with repeated measures. RESULTS: Average core temperature was significantly higher in H compared to RT (38.1°C ± 0.01° vs. 37.9°C ± 0.08°, P < 0.05) during recovery. Glycogen was not different at 0 and 2 hours post exercise. However, at 4 hours post-exercise muscle glycogen was significantly higher in RT vs. H (105 ± 28 vs. 88 ± 24 mmolxxxkg-1 wet weight, respectively). Blood glucose levels were similar between H and RT for the first two hours, but showed lower values (P < 0.05) in RT compared to H at time points 150, 180, and 240 minutes into recovery. There was no difference in respiratory exchange ratio between treatments, but RER was higher during the second half of recovery compared to the first for both trials (0.905 ± 0.001 vs. 0.962 ± 0.010 for hours 2 and 4, respectively, P < 0.05). CONCLUSION: Glycogen resynthesis during recovery is impaired in a hot environment, perhaps due to decreased glucose transport into the muscle. Supported by Air Force Research Laboratories, FA8650-06-1-679.