Acclimation Interventions for Olympic competition in hot and humid environments

The Tokyo 2020 Olympic Games were due to be the hottest on record, with hot (>30 °C) and high-humidity environmental conditions (70-90% relative humidity). Olympic Distance Triathlon comprises a 1.5 km swim, a 40 km bike ride, and a 10 km run performed successively. Prolonged exercise in the heat produces greater physiological and perceptual strain compared to exercising in temperate environmental conditions at the same intensity. Athletes competing in middle- and long-distance events are at a higher risk of reductions in exercise performance and incidence of heat illness compared to short distance events in the heat. Heat acclimation (HA) is the most effective countermeasure to protect athlete health and improve performance. Research on applied and effective HA strategies which confer the necessary heat adaptation responses while still conforming to the ecological training needs of highly trained athletes is limited. The first study (Chapter 4) of this thesis established the reliability of novel blood biomarkers and classical physiological and perceptual markers of heat stress during a new cycling heat stress test (HST) which fixes the intensity relative to body mass. The test offers a reliable assessment tool to evaluate the effectiveness of HA protocols employed. Chapter 5 evaluated whether 5-days isothermic HA was an effective preparation strategy for the Tokyo 2020 Olympic Games in endurance trained athletes. Reduced cardiovascular and perceptual strain, plasma volume expansion and an increase in sweat loss were evident. However, there was no change in body temperature or surrogate biomarkers of physiological stress. Chapter 6 investigated the effectiveness of a novel and ecologically valid 8-day HA strategy which combined modes of HA; isothermic HA and post-temperate exercise hot water immersion (HWI). There was reduced thermal, cardiovascular, and perceptual strain after 4-days HA, with no further improvement at day 8 of HA. Diminished sympathetic activity and fluid-regulatory stress were evident after 8-days HA. However, no change in performance was demonstrated during a 20-km cycling time trial in the heat. This thesis provides practitioners and coaches within British Triathlon Federation a reliable assessment tool of heat dissipation capacity in Tokyo specific environmental conditions. 5-days isothermic HA induced partial HA, affording athletes a time-efficient approach for rapid adaptation. However, a combined HA protocol of isothermic HA and HWI over 4 and 8-days induces superior thermoregulatory, perceptual, and biochemical adaptations. Hence, is the recommended approach for elite triathletes prior to competition at the Tokyo 2020 Games.