INTRODUCTION:
Hot-water immersion (HWI) after training in temperate conditions has been shown to induce thermophysiological adaptations and improve endurance performance in the heat, however, the potential additive effects of HWI and training in hot outdoor conditions remain unknown. Therefore, this study aimed to determine the effect of repeated post-exercise HWI in athletes training in a hot environment.
METHODS:
Thirteen (9 female) elite/pre-elite partially heat acclimatized racewalkers completed a 15-day training program in outdoor heat (mean afternoon high temperature=34.6°C). Athletes were divided into two groups matched for VO2max and 10,000 m walking performance time that completed either HWI (40°C for 30-40 min) or seated rest in 21°C (CON), following 8 training sessions. Pre-post testing included a 30-min fixed-intensity walk in heat, laboratory incremental walk to exhaustion and 10,000 m outdoor time-trial.
RESULTS:
Training frequency and volume was similar between groups (P=0.54). Core temperature was significantly higher during immersion in HWI (38.5 ± 0.3) than CON (37.8 ± 0.2°C; P<0.001). There were no differences between groups in resting or exercise rectal temperature or heart rate, skin temperature, sweat rate, or the speed at Lactate Threshold 2, VO2max or 10,000 m performance (P>0.05). There were significant (P<0.05) pre-post differences for both groups in submaximal exercising heart rate (~11 bpm) sweat rate (0.34-0.55 L.h-1) and thermal comfort (1.2–1.5 arbitrary units), and 10,000 m racewalking performance time (~3 min).
CONCLUSION:
After a 15-day heat training intervention, we observed significantly improved submaximal exercising heart rate, sweat rate, and thermal comfort, as well as improved 10,000 m racewalking performance in both groups. However, the addition of HWI did not further enhance heat adaptation or performance in partially heat-acclimatized athletes. Physiological adaptation appeared to be optimized from training in hot conditions alone.