Background A hot environment is associated with an increase in core temperature and dehydration. However, there are minimal data investigating the time course of changes in oxidative stress and DNA in response to cycling in a hot environment. Additionally, it is not known whether there is a critical point in core temperature for the production of oxidative stress or DNA modification. Subsequently, this research investigated the time course of changes in markers of oxidative stress and DNA modification during and after exercise in a hot environment. Methods Eight cyclists (age=30.9±2.2yrs; height=177.9±4.1cm; mass=74.5±4.5kg) completed a cycling VO2max in hot conditions (35°C, 70%RH) to determine 60% of peak power output (PPO). One week later they returned and cycled at this intensity until they reached a core temperature of 38.5°C. Blood was sampled before, during, and after (0, 10, 25, 35, post 10 and post 20 mins) exercise to determine changes in oxidative stress and DNA. Statistical analysis was completed using linear mixed models with a level of significance set at p≤0.05. Results Cycling at 60% of PPO until core temperature reached 38.5°C resulted in a significant increase in oxidative stress over the exercise bout. Data showed that oxidative stress increased during exercise period (0-10, 25, 35 min [0 min post]) and decreased from 0-post to post 20 min recovery. After correcting for multiple comparisons, there was a tendency towards significance from 0 mins to the completion of the exercise bout. However, no changes were observed in the modification of DNA during exercise or recovery. No relationship was observed among the changes in blood markers and core temperature. Conclusion Research shows that regular exercise protects against exercise-induced changes in oxidative stress and DNA. This research shows that this relationship extends to exercising in a hot environment. Changes in oxidative stress appeared to be more sensitive to exercise duration than core temperature. Furthermore, these data showed that there was no critical core temperature for the development of oxidative stress. However, the current project was limited to a maximum core temperature of 38.5°C. Future research should continue exercise beyond this point to develop a clearer understanding.


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