Neither Short-term Sprint nor Endurance Training Enhances Thermal Response to Exercise in a Hot Environment

Abstract

Improvements in fitness from a brief period of physical training may elicit sufficient physiological adaptations to decrease thermal strain during exercise in the heat. This study tested heat adaptation from short-term endurance (ET) and sprint-interval (SIT) training in moderately fit individuals. The ET group (n = 8) cycled at 65% for 8 sessions (4 sessions each at 60 and 90 min, respectively) over two weeks, while the SIT group (n = 8) performed repeated 30-s Wingate sprints (resistance 7.5% body mass; 4 sessions each of 4 and 5 sprints, respectively). and heat stress testing (HST; 60 min cycling at 65% at 35ºC, 40% relative humidity) were performed pre- and post-training. increased by 11% (p = 0.025) and 14% (p = 0.020) for the ET and SIT groups post-training, respectively. Thermal stress was similar pre- and post-training, with no significant difference in the rate of whole-body metabolic heat production (p = 0.106) for either group post-training. Cardiovascular improvement was evident with both ET and SIT, with a significant mean decrease (p = 0.014) in HR for both groups (ET: 146 ± 15 beats·min⁻¹pre vs. 142 ± 12 beats·min⁻¹post; SIT: 149 ± 15 beats·min⁻¹pre vs. 146 ± 12 beats·min⁻¹post) during the HST post-training. However, mean sweat loss (p = 0.248) and the rise in core temperature (p = 0. 260) did not change significantly comparing pre- and post-training HST. While short-term ET and SIT both induced significant improvements in aerobic fitness and decreased cardiovascular strain, neither elicited improved thermal responses during exercise in the heat and do not replace heat acclimatization.

Keywords:

• temperature regulation
• aerobic training
• sprint training
• heat adaptation

ACKNOWLEDGMENTS

The authors express their gratitude to the participants in the experiments. This project was funded by the Natural Science and Engineering Research Council (NSERC) of Canada through a Discovery Grant (227912-07, S.S. Cheung). S.S. Cheung was supported by a Canada Research Chair.