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Heat management strategies in elite rugby sevens

The purpose of this thesis was to develop and implement heat management strategies for international elite men’s and women’s rugby sevens teams competing in hot and humid conditions. The first three of six experimental chapters aimed to characterise the physiological, perceptual, and performance perturbations that undertaking rugby sevens specific exercise in hot and humid conditions involves. The following three experimental chapters built upon these characterisations by investigating practical, training-integrated interventions, designed to alleviate the stressors that collectively impair performance. Study One (Chapter Three) investigated the validity of two practical measures of core and skin temperature (T꜀; Tsₛₖ during exercise in hot and humid conditions, to identify a measurement tool that could be used during subsequent investigations within the thesis. A tympanic thermometer (to measure tympanic temperature; Tₜyₘₚ) provided sufficient levels of validity compared to gold-standard gastrointestinal T꜀ measurement, while a portable infrared thermometer was not valid for measurement of Tₛₖ, compared to the criterion measure of hard-wired skin thermistors. Study Two (Chapter Four) involved the characterisation of T꜀, and physiological and performance characteristics that mediate T꜀ change across a rugby sevens tournament played in hot and humid conditions. Commonly measured variables such as playing minutes, high-speed distance, and total distance significantly predicted post-game T꜀ during an international rugby sevens tournament played in hot and humid conditions. In turn, post warm-up Tc significantly predicted post-game T꜀. Moreover, during each tournament day sequential increases in mean T꜀ post warm-up were shown, and all post-baseline measures were greater than baseline on day one and day two, indicative of a cumulative increase in T꜀ across the tournament, particularly during non-competition exercise. Study Three (Chapter Five) investigated the differences in heat stress between high-intensity running in temperate and hot conditions, while also assessing the application of an off-feet (cycling) heat response test that would be practical to use within the training weeks of an elite rugby sevens team. Acute heat stress resulted in large increases in physiological and perceptual thermal strain when compared to the same exercise stimulus performed in temperate conditions. Furthermore, these increases in thermal strain were associated with a large performance decrement. When comparing running to cycling heat response tests, moderate – large physiological differences were evident, whereas no clear effects on any variables associated with perceptual thermal heat stress were observed. High-intensity running in the heat induces high physiological strain and additional mechanical load that may not be suitable for elite team-sport athletes, meanwhile, high-intensity cycling in the heat induces thermal strain sufficient to drive adaptation and can replicate the perceptual, but not the physiological stress associated with high-intensity running in the heat. Study Four (Chapter Six) investigated the effectiveness and retention of 10-days of mixed active/passive heat acclimation (HA) integrated within two-weeks of an elite male rugby sevens team training program. Five days of mixed-methods HA elicited some typical physiological, perceptual, and performance adaptations, with an additional five days eliciting further improvements in T꜀, sweat rate, and performance during an intermittent sprint heat response test. Furthermore, most adaptations were retained after 16-days of normal training with no additional environmental heat exposure, providing initial evidence for the efficacy of a practical, and ecologically valid, mixed-methods HA protocol within an elite teams training program. Study Five (Chapter Seven) examined physiological, perceptual and performance changes during and following 10-days of (primarily) passive HA integrated into an elite female rugby sevens teams training program. Meaningful changes in resting and submaximal Tₜyₘₚ were achieved only after the full 10-day HA protocol, however these were not well-retained after 15 days without any further heat stimulus. Concurrently, meaningful increases in repeated-sprint peak power output were evident, while no sudomotor or cardiovascular changes were apparent during or post HA. Ten days of (primarily) passive HA elicits minor thermoregulatory and performance benefit when integrated into an elite team’s training program. However, such a protocol does not provide a sufficient thermal impulse for adaptations to be retained after 15-days with no further heat stimulus. Study Six (Chapter Eight) investigated the application of internal and external cooling strategies delivered via the use of ice slurry ingestion and the application of ice towels to the head, neck, and face before and during a repeated high-intensity exercise heat response test within an international elite men’s rugby sevens team. The use of this cooling strategy resulted beneficial physiological changes and beneficial changes in indices of thermal perception. Furthermore, there was a small increase in mean time-trial power output during compared to undertaking no cooling. With very limited previous research on heat management strategies in rugby sevens, particularly in an elite setting, the research within this thesis is among the first to address these critical areas of preparation and performance in an elite rugby sevens context. It is recommended that practitioners include a combination of practical heat acclimation and cooling strategies within their heat management plan when performing in hot conditions.
Type of thesis
The University of Waikato
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