The effects of post-training hot water immersion on concurrent training load and treadmill running performance in the heat : a thesis presented in partial fulfilment of the requirements for the degree of Master of Sport & Exercise in Exercise and Sport Science at Massey University, Albany, New Zealand

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Background: Team-sport athletes of both elite and sub-elite status are often required to travel to hot and/or humid environments for competition; however, preparing for these environmental challenges can be difficult within a team-sport setting. Heat acclimation (HA) strategies for team-sports can typically involve the use of expensive equipment, or travel in advance of competition to naturally acclimatise to the competition environment; these may also affect the quality of concurrent training. These logistical challenges often faced by team-sports when preparing for competition in hot environments often dictate what is (un)available to them. Post-training hot water immersion (HWI) has emerged as a passive approach that is logistically friendly for sporting teams to use during a preparatory period for competition in the heat. Aim: To investigate if 6-days of post-training HWI is an effective HA strategy for sub-elite, male, team-sport athletes, has any detrimental effects on concurrent training load and if it can improve aerobic capacity in the heat. Methodology: In a randomised control study, fifteen, non-acclimatised, moderately-trained males performed an intermittent running protocol in temperate outdoor conditions (18°C, 67% RH) for six consecutive days followed by a post-training cool-down (CON; n=8) or an additional 40 min of HWI in 38°C (n=7). Three days before and two days following the intervention, participants completed a RAMP treadmill run in the heat (33°C, 30% RH). Results: The HWI group displayed a reduced mean heart rate (p=0.02) during immersion from day-1 to day-6 (by 14±10 beats‧min⁻¹) and improved feelings (by 0.9±0.5 AU; p=0.003). Daily HWI had no detrimental effects on concurrent training as no significant differences (all p<0.05) were found between groups for total distance run, session RPE and the composite measure of training load (duration x RPE). Treadmill VO2peak improved from pre-post for the HWI group (by 2.1 ml‧kg⁻¹‧min⁻¹or 4.2%; p=0.003) but not the CON group (0.2 ml‧kg⁻¹‧min⁻¹ or 0%; p=0.88). Conclusions: Six consecutive days of post-training HWI induces partial HA in moderately trained team-sports athletes with no detrimental effects on concurrent training load. This provides a practical acclimation strategy for sporting teams to implement when preparing for competition in the heat that acknowledges the logistical challenges often faced.
Exercise, Physiological aspects, Heat, Water immersion, Physiological effect