Environmental temperature and glycogen resynthesis
Journal Title (Medline/Pubmed accepted abbreviation):  Int J Sports Med
Year: 2010
Volume: 31
Page numbers: 561-566
doi (if applicable): 

Summary of Background and Research Design

Hypothesis:Muscle glycogen resynthesis would be impaired in a hot environment versus room temperature environment during the 4-h period following exercise.

Subjects:Subjects were 9 healthy, recreationally active males (mean age = 24 y, mean weight = 79 kg, mean body fat percentage = 16.8%)

Experimental design:Randomized, crossover

Treatments and protocol:The subjects completed a preliminary trial in which VO2 max and maximal power output were determined. Following the preliminary testing, the subjects visited the laboratory on 2 separate occasions and performed a 1-h cycle ride at 60% of maximum work output in a temperature-controlled chamber (32° C) each time. A carbohydrate beverage (dextrose, 1.8 g/kg body weight) was supplied at 0 and 2 h post-exercise.    On one visit, the subjects remained in the temperature controlled chamber at 32 ° C for the 4-h recovery period (H) and for the other visit, the subjects were in a room temperature (22° C) environment (RT). Muscle biopsies for glycogen determination were taken at 0, 2, and 4 h post-exercise. Core temperature was monitored continuously before and during exercise and for 4 h post exercise. Carbohydrate oxidation was measured at 2 and 4 h post-exercise. Blood was sampled immediately after exercise and at 30, 60, 120, 150, 180, and 240 min after exercise.

Summary of research findings:
Core temperatures were consistently elevated (about 0.4° C) in the H condition vs. RT from 30-240 min intervals postexercise. Muscle glycogen resynthesis was not different between the two temperatures at the 2-h post-exercise interval, but was ~18% lower at the 4-h interval for the H vs. RT condition. Carbohydrate oxidation was increased at both the 2- and 4-h post-exercise time points for the H vs. RT environment. Blood glucose levels were higher for H compared with RT at 150, 180, and 240 min postexercise.  There were no significant changes in insulin for the two temperatures.

Interpretation of findings/Key practice applications:

The authors suggest that recovery in a hot environment may impair glycogen resynthesis after exercise relative to a lower temperature environment. As such, athletes may want to exercise additional care (e.g., higher carbohydrate intakes, better hydration and cooling strategies) to ensure rapid muscle glycogen recovery in hotter environments. However, two key limitations of this study are: 1) the small number of subjects (n = 9); and 2) the selection of subject who were not highly trained or conditioned for exercise in the heat. There were also no markers of hydration status measured in the study.
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