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% [Formula: see text] 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). [Formula: see text] and heat stress testing (HST; 60 min cycling at 65% [Formula: see text] at 35ºC, 40% relative humidity) were performed pre- and post-training. [Formula: see text]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(-1)pre vs. 142 ± 12 beats·min(-1)post; SIT: 149 ± 15 beats·min(-1)pre vs. 146 ± 12 beats·min(-1)post) 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.

Thermoregulatory Adaptations following Sprint Interval Training

“…Some studies investigating SIT (McGarr et al, 2014;Trilk, Singhal, Bigelman, & Cureton, 2011) or short-term high-intensity training sessions (Rodas et al, 2000) have found improvements in cardiorespiratory fitness while others (Burgomaster, Hughes, Heigenhauser, Bradwell, & Gibalam, 2005), like our study, have not. The reason for the discrepant findings is uncertain but is likely related to differences in the exercise protocol used and the participants tested.…”

“…The reason for the discrepant findings is uncertain but is likely related to differences in the exercise protocol used and the participants tested. Participants in the Burgomaster et al (2005) and McGarr et al (2014) studies were ''recreationally active,'' exercising 2-3 times per week (e.g., jogging, cycling, aerobics), yet V O 2peak increased after SIT in the latter but not the former of these two investigations. Participants in the Trilk et al (2011) study were sedentary overweight/obese women, so it is not surprising cardiorespiratory fitness increased in these participants considering that it was low to begin with.…”

“…Nonetheless, some sources have reported the effectiveness of shorter (either duration of exercise or number of days or both) protocols (Chalmers, Esterman, Eston, Bowering, & Norton, 2014;Charlot et al, 2017;Garrett, Creasy, Rehrer, Patterson, & Cotter, 2012;Garrett, Goosens, Rehrer, Patterson, & Cotter, 2009;Garrett et al, 2014;Houmard et al, 1990;Kelly, Gastin, Dwyer, Sostaric, & Snow, 2016;Petersen et al, 2010). Of these, only a couple of studies involved short-duration exercise (e.g., high-intensity interval training or SIT), with mixed results (Kelly et al, 2016;McGarr, Hartley, & Cheung, 2014). Kelly et al (2016) investigated the effect of five sessions of high-intensity interval training (3 6 5 min bouts with intensity alternating between 30% and 90% V O 2max every 30 s) spread over nine days on heat acclimation adaptations in moderately fit Australian football players.…”

“…Perceptual responses (perceived exertion and thermal comfort) improved, but other markers of heat acclimation (heart rate, core temperature, sweat rate) were unaffected. McGarr et al (2014) had moderately fit participants perform 4-5 repeated Wingate Anaerobic Tests (WAnT) over eight sessions in two weeks. Heat stress tests were administered before and after the training (60 min cycling at 65% peak oxygen uptake in 35˚C, 40% rh).…”

“…The Kelly et al (2016) study utilized submaximal exercise intensities (and, therefore, a lower internal heat stimulus compared to maximal intensity exercise) and only five days of heat exposure and the McGarr et al (2014) study involved training sessions in a temperate environment that would not have caused elevations in skin temperature needed to optimize heat acclimation (Regan, Macfarlane, & Taylor, 1996). Additionally, the participants in both studies were characterized as ''moderately fit.''…”