| Context. Exercise in the heat causes physiological and perceptual changes which can indicate decreased performance or heat illness. Understanding the signs of heat stress is important for those who exercise in the heat. Objective. To examine the effects of uncompensable heat stress on physiological and perceptual measures and time to exhaustion. Design. Randomized, crossover design. Setting: Exercise physiology laboratory. Patients or Other Participants. Ten euhydrated, sodium-balanced participants (6 male, 4 female, age=27.9 +/- 7.76 years, height=172.72 +/- 12.54 cm, mass=70.27 +/- 15.79 kg) completed this study. Intervention(s). Participants completed 2 trials: a control trial (C) in temperate conditions, and a heat stress trial (HST) in hot, humid conditions. Participants exercised at 2.25 m/s on a treadmill until fatigue or core temperature of 40°C was reached. Main Outcome Measure(s). Body mass was measured pre-, post-, and after every 15 min of exercise. Heart rate, core temperature, perceived exertion, and perceived fatigue were assessed pre-exercise and after every 5 min of exercise. Blood samples were collected pre-, post-, and after every 30 min of exercise. Urine samples were collected pre-end post-exercise. VO2max was estimated from 12 min run distance. Results. Time to exhaustion was decreased in the HST (p = 0.035). Core temperature at 45 min (p < 0.001) and heart rate at 30 min (p = 0.034) were higher during the HST. Physiological strain index was higher in the HST at 45 min (p = 0.009). Sweat rate was not related to time to exhaustion. Conclusions. Environment had a negative effect on physiological, but not perceptual measures. Physiological strain index scores were higher than previously reported for euhydrated individuals. Monitoring these variables and understanding their context is important for those who exercise in the heat.;Key Words: Physiological strain index, hyperthermia, fatigue. |
