Kjertakov, Metodija (2019) The role of heat as a conditioning stimulus in endurance athletes. Research Master thesis, Victoria University.

Abstract

Objective: The purpose of this study was to investigate the effects of regular postexercise hot water immersion (HWI) on selected physiological adaptations and on exercise performance in a temperate environment in trained road cyclists. Methods: Fourteen male cyclists were assigned to either an HWI (n = 7) group or a control (CON, n = 7) group. Both groups completed 9 high-intensity interval training sessions (over 3 weeks), with each training session followed by sitting in a water tub for 30 min. Participants from the HWI group were immersed in 42°C water, whereas a thermoneutral water temperature of 34°C was used for the CON group. Core and intramuscular temperature were continuously recorded during the first water immersion session and for 30 min post-session. Before and after the intervention, the cyclists performed a 20-km time trial test and an incremental test to exhaustion to determine lactate turn point, maximal oxygen consumption and peak power output. Venous blood at rest was sampled pre- and post-intervention to assess changes in plasma volume. Muscles biopsies were obtained from the vastus lateralis pre- and post-intervention to assess changes in mitochondrial function. Variables were analysed using t-test and two-way repeated measures analysis of variance. Results: Intramuscular temperature was significantly higher in the HWI than in the CON group at the end of the water immersion treatment (37.8 ± 0.4 vs 36.2 ± 0.5 °C, p=0.001) and 30 min post-immersion (36.7 ± 0.4 vs 35.1 ± 1.2 °C, p=0.01). In addition, HWI group had significantly higher core temperature immediately post-immersion than the CON group (37.8 ± 0.4 vs 37.1 ± 0.2 °C, p=0.01). However, all other measures were not significantly different between the groups. Nevertheless, there was a significant improvement in 20-km time trial performance in both the HWI (2009.8 ± 147.3 vs 1977.5 ± 134.5 seconds, p=0.01) and the CON group (2010.4 ± 182.3 vs 1974.2 ± 185.7 seconds, p=0.04). Conclusion: Three weeks of high intensity interval training led to an improved 20-km time trial performance, but the post-exercise HWI protocol used in this study did not provide additional performance benefits.

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