Acute intermittent heat exposure with more frequent and shorter cooling breaks enhances performance and elicits comparable physiological responses to continuous heat exposure

INTRODUCTION & AIMS Heat acclimation (HA) is critical to mitigate the adverse effects of heat on exercise performance. While these methods yield physiological adaptations to heat, it also results in greater internal training load. This can potentially compromise training quality and lead to overreaching. Therefore, there is a need for HA protocols that address situations where training quality is crucial, yet the heat stimulus is necessary. The aim of this study was to investigate the influence of shorter, more frequent rest breaks with per-cooling (PerC) as an alternative HA session on physiological, perceptual, and self-paced maximal cycling performance, compared to continuous heat exposure. METHODS Thirteen participants completed one continuous and three intermittent heat exposure (IHE) maximal self-paced cycling protocols matched for total exercise and rest duration, in a random order in heat (36°C, 80% relative humidity): 1 x 60-min exercise (CON), 3 x 20-min exercise with 7.5-min rest between sets (IHE-20), 4 x 15-min exercise with 5-min rest between sets (IHE-15), 6 x 10-min exercise with 3-min rest between sets (IHE-10). Mixed-method PerC (crushed-ice ingestion and cooling vest) was applied during rest periods of all IHE protocols. RESULTS Total distance completed was greater in IHE-10, IHE-15, and IHE-20 compared to CON (+11%, +9%, and +8%, respectively), with no difference observed between IHE protocols. Total time spent above 38.5°C core temperature (Tc) was longer in CON compared to IHE-15 and IHE-20 (+62% and +78%, respectively), but similar to IHE-10 (+5%). Furthermore, a longer time above 38.5°C Tc occurred in IHE-10 versus IHE-15 and IHE-20 (+54% and +69%, respectively). Sweat loss did not differ between conditions. CONCLUSION Intermittent heat exposure with PerC may be a viable alternative HA protocol in situations where training quality takes precedence over thermal stimulus, or when both factors hold equal priority.