Effects of 4-Days Short-Term Isothermic Heat Acclimation with Permissive Dehydration on Recreational Female Endurance Runners

Chong, Weng Foong (2025) Effects of 4-Days Short-Term Isothermic Heat Acclimation with Permissive Dehydration on Recreational Female Endurance Runners. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Standard heat acclimation (HA) protocols typically involve 60 to 90 minutes of daily heat exposure for more than five consecutive days. However, optimizing the minimum effective duration and intensity of HA remains crucial. This study aimed to investigate the effects of a 4-day short-term isothermic heat acclimation (IHA) protocol, combined with permissive dehydration, on running performance in recreational female endurance runners. Seven recreational female runners (age: 25.0 ± 5.8 years old; height: 152.4 ± 5.1 cm; weight: 49.1 ± 5.5 kg; weekly mileage: 20.3 ± 6.0 km; VO2max: 41.3 ± 6.8 ml·kg⁻¹·min⁻¹) completed four consecutive days of 90-minute IHA sessions, maintaining a core temperature (Tcore) above 38.5 °C, under environmental conditions of 39.9 ± 0.3 °C and 39.4 ± 4.1% relative humidity, with fluid intake restricted. A heat stress test (HST) was conducted before and after the intervention, consisting of 30 minutes of treadmill running at 65% VO2max, followed by a graded exercise test (GXT) to exhaustion in hot conditions (ambient temperature: 35.4 ± 0.3 °C; RH: 47.5 ± 4.2%). Post-IHA, significant improvements were observed in time to exhaustion (TTE) during the GXT under heat stress (Pre: 12.0 ± 2.1 min; Post: 13.7 ± 2.7 min; p = .011). Heart rate during the 30-minute steady-state run was significantly lower post-intervention (Pre: 174 ± 16.4 bpm; Post: 164 ± 15.7 bpm; p = .005). Thermoregulatory adaptations included a significantly lower skin temperature at the end of the 30-minute run post-IHA (Pre: 36.85 ± 1.02 °C; Post: 36.03 ± 0.57°C; p = .035). Although post-test core temperature was lower and sweat rate higher, these differences were not statistically significant (p > .05). Among perceptual responses, only final thermal sensation during the HST showed a significant cooler perception (p = .047). In conclusion, these findings suggest that a 4-day short-term IHA protocol with permissive dehydration can elicit meaningful physiological, performance, and perceptual adaptations in recreational female endurance runners.