EFFECTS OF HEAT ON OXIDATIVE STRESS MARKER (REDUCED TO OXIDIZED GLUTATHIONE RATIO), SELECTED PHYSIOLOGICAL RESPONSES AND RUNNING TIME-TRIAL PERFORMANCE AMONG RECREATIONAL ATHLETES
Background: The increased production of free radicals during exercise has been shown to be associated with oxidative stress that impaired exercise performance. However, information on the exercise-induced oxidative stress among individuals living in the hot and humid environment is limited. Thus, the present study was carried out to investigate the effects of heat on oxidative stress, selected physiological responses and time-trial performance amongrecreational athletes.
Materials and Methods: Twelve male recreational athletes (Age: 23.1 ± 2.1 years old; Body weight: 64.0 ± 8.7 kg; VO2max: 54.3 ± 4.6 mL.kg-1.min-1) were recruited and assigned to perform prolonged running at 70% of their respective VO2max for 60 min and immediately followed by a 20 min time-trial performance on a motorized treadmill in a randomized cross-over trial. The two trial conditions were in the heat (H trial; 32˚C room temperature, 70% relative humidity) and thermoneutral (N trial; 25˚C room temperature, 70% relative humidity) environments. During the trials, oxygen uptake (VO2), heart rate, core body temperature and rate of perceived exertion (RPE) were recorded. Blood samples were drawn before warm-up, at beginning of exercise, and every 20 min of exercise. The samples were analyzed for reduced glutathione (GSH) and oxidized glutathione (GSSG).
Result: There was no significant difference in the GSH: GSSG ratio between trials (p=0.963), where the mean GSH:GSSG ratio at the end of exercise in the N and H trials were 25.4 ± 6.9 and 27.7 ±13.6, respectively. Heart rate was significantly higher in the H trial from the 30th min until the end of the run but was not different from the N trial during the time trial performance. There were also no differences between trials in core body temperature and RPE between trials. The oxygen uptake was significantly higher in the N trial compared to the H trial. The running distance in the H trial was 0.31 km shorter (p< 0.001) compared to the N trial.
Conclusion: These results indicated that prolonged running either in the heat or thermo-neutral environment did not seem to enhance oxidative stress. Additionally, running in the heat did not have an effect on core body temperature and RPE compared to a thermoneutral environment among the recreational athletes. However, the time-trial performance of these athletes was impaired in the hot and humid environment.Keywords: Heat, free radicals, oxidative stress, GSH:GSSG ratio, exercise performance