Bovalino, Damien (2025) Effects of short-term heat acclimation on endurance cycling performance in the heat. Research Master thesis, Victoria University.

Abstract

Heat training has been established as a tool to maximise physiological adaptations and enhance endurance performance in both hot and cool environmental conditions. However, recent research in the field of heat acclimation (HA) has uncovered physiological variances between sexes in their response to established heat protocols. The primary aim of this research was to determine the effects of short-term HA (5 days, 110 mins, 40°C and 40% relative humidity (RH)) on endurance cycling performance and physiological markers of HA - core temperature (°C), peak skin temperature (°C), heart rate (HR) (beats·min-1), blood plasma volume (Δ%) and sweat rate (L·h-1), in hot environments. Through the use of an emerging protocol, controlled heart rate, in tier two trained status females and males. The hypothesis tested was that five days of 110 mins of exercise at a controlled heart rate equivalent to heart rate at 65% of V̇O2max, in conditions of 40°C and 40% RH would significantly improve endurance cycling performance in the heat (20 km time trial at 33°C & 40% RH), and elicit significant improvements in physiological markers of HA as measured pre and post training using a heat stress test (40% of maximal aerobic power (MAP) for 30 mins in conditions of 40°C & 40% RH). Sixteen (eight females, eight males) participants who were undertaking at least three one hour plus sessions of cycling per week completed all HA sessions, resulting in improved time trial power (females: 4.9%, p < 0.001; males 6.7%, p = 0.001) and reduced duration (females: -2.0%, p = 0.004; males -2.6%, p = 0.001). Females saw significant improvement to markers of HA; peak HR reducing 15.9 ± 8.0 beats·min-1 (-9.6%, p = 0.001), peak core temperature reducing 0.33 ± 0.17°C (-0.9%, p = 0.002), thermal comfort reducing from slightly uncomfortable towards neutral (p = 0.003), thermal sensation reducing from hot to warm (p = 0.049) and RPE reducing from light towards very light (p = 0.020). While males saw significant improvement in peak core temperature reducing 0.30 ± 0.29°C (-5.5%, p = 0.024), thermal sensation reducing from hot to warm (p = 0.003) and tendency towards significance for peak HR reducing -8.0 ± 9.7 beats·min-1, plasma volume expansion of 3.5% ± 10.9% and thermal comfort reducing from slightly uncomfortable towards neutral. These findings demonstrate the practical benefits for athletes in utilising a controlled heart-rate based HA protocol, to reduce performance decrement in the heat.

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