- Title
- Performance, physiological and perceptual effects of cooling endurance athletes in the heat
- Creator
- Stevens, Christopher
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2016
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The purpose of this thesis was twofold. Firstly, to assess the validity and reliability of a non-motorised treadmill (NMT) ergometer for the assessment of self-paced endurance running performance. Secondly, it aimed to compare the effect of practical external, internal and mixed-method pre-cooling and mid-cooling interventions on endurance running performance in the heat whilst examining their influence on related physiological and perceptual responses. Moderately trained endurance runners completed a range of endurance running time trials across five novel experimental studies. In study one, a 5 km running time trial performed on a NMT was compared to a time trial performed overground to establish validity and in study two, repeated 5 km running time trials were performed on the NMT to establish reliability. Performance time was strongly correlated (r=0.82, ICC=0.86) between NMT and overground running, despite running time being significantly longer on the NMT (21.1 ± 2.1 min vs. 25.6 ± 2.2 min for overground and NMT, respectively; P<0.001). The repeated 5 km time trials (25.4 ± 2.7 min vs. 25.3 ± 2.7 min for trials 1 and 2, respectively) demonstrated a low CV of 1.2% and high ICC of 0.99. In studies three and four, comparisons were made between external (cold-water immersion and intermittent facial water spray) and internal interventions (ice slurry ingestion and menthol mouth rinse) on self-paced NMT running performance in the heat (33°C). In study five, the pre-cooling (cold-water immersion and ice slurry ingestion) and mid-cooling (facial water spray and menthol mouth rinse) interventions were combined, within a pre-loaded NMT running time trial (20 min at 70% VO₂max followed by a 3 km time trial) in the heat (33°C). In studies three-five, rectal and skin temperatures, cardiorespiratory responses, muscular activation, sweat rate and perceptual responses were measured as well as the concentrations of blood lactate and prolactin. In study three, 5 km running performance on the NMT was significantly faster with both cold-water immersion (24.5 ± 2.8 min; P=0.01) and water spray (24.6 ± 3.3 min; P=0.01) when compared against the control (25.2 ± 3.2 min). In study four, 5 km running performance was significantly improved with menthol rinse (25.3 ± 3.5 min; P=0.01) but not ice slurry ingestion (26.3 ± 3.2 min; P=0.45) compared to control (26.0 ± 3.4 min). In study five, 3 km running performance was significantly improved with mixed-method mid-cooling (13.7 ± 1.2 min; P<0.01) and all interventions combined (13.7 ± 1.4 min; P=0.04) but not mixed-method pre-cooling (13.9 ± 1.4 min; P=0.24) compared to control (14.2 ± 1.2 min). There were also no significant performance improvements between cooling conditions across all studies. With the exception of ice slurry ingestion, all cooling strategies significantly improved the perception of thermal sensation (P<0.05). The external interventions significantly increased muscular activation (P<0.05) and when the strategies were combined, there were significant reductions in blood prolactin concentration (P<0.05) suggesting both an attenuated release of the stress hormone and more favourable neurotransmitter activity. Runners were consistently slower on the NMT than field-based trials, and as such it should not be used to measure performance over a specific distance. However, the strong correlations suggest that superior overground performance was reflected in relative terms on the NMT. Similarly, the repeated NMT trials demonstrated high reliability and taken together, the data demonstrate that the NMT is a useful tool for the assessment of endurance running performance in the laboratory. With the exception of ice slurry ingestion, all of the cooling interventions improved endurance running performance by a similar magnitude and are likely beneficial for athletes. Athletes should focus on the use of mid-cooling with the aim to maximise reductions in thermal sensation for the greatest effect. Attenuated prolactin release as measured in the periphery may represent more favorable neurotransmitter activity in the brainstem and improved thermoregulatory control, as well as enhanced arousal and motivation. These adjustments may be part of an integrated central response to cooling involving attenuated afferent feedback from peripheral thermoreceptors, inhibited secretion of stress hormones, and up-regulation of self-selected running speed. Future research should compare the effects of a single cooling intervention both prior to and during exercise and further investigate the central aspects of endurance performance with cooling.
- Subject
- running; thermoregulation; pre-cooling; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1314612
- Identifier
- uon:22790
- Rights
- Copyright 2016 Christopher Stevens
- Language
- eng
- Full Text
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