Date of Award

2012

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Exercise and Health Science

Faculty

Computing, Health and Science

First Advisor

Adjunct Professor Paul B. Laursen

Second Advisor

Dr. Chris R. Abbiss

Third Advisor

Professor Louise M. Burke, Dr. David T. Martin

Abstract

Whole-body precooling can improve endurance exercise performance, especially in the heat; however there are logistical considerations that restrict the use of various precooling strategies prior to actual competition. Precooling is proposed to collectively reduce deep skin and body temperature and in effect, increase the heat storage capacity of an athlete, thereby allowing a greater amount of work to be completed prior to attainment of a critical core temperature. While there is a sound theoretical basis for implementing precooling to improve cycling time trial performance in the heat, the practicalities of employing effective precooling strategies in the field warrant further investigation. The purpose of this thesis was to investigate the effectiveness of various practical precooling strategies for reducing core temperature and improving cycling time trial performance in hot (32-35ºC; 50-60% r.h.) and temperate (20-22 ºC; 50-60% r.h.) conditions.

The first three studies of this thesis involved the manipulation of body temperature via a range of precooling strategies that were applied under hot and humid environmental conditions. In study 1, eight precooling strategies involving external application or internal ingestion of cold water and ice were evaluated for their effectiveness in lowering deep body temperature, with due consideration regarding their application in a practical setting. The novel strategy identified in this study, which involved the combined application of iced towels and ingestion of an ice-slurry (“slushie”) made from sports drink, was then compared with an established cooling strategy (Study 2). Both the new and established precooling strategies achieved noticeable cooling effects (moderate and very large, respectively) but only the new strategy enhanced mean power output (3%, 8W) during a 46.4 km laboratory-based cycling protocol, with performance improvements detected in the second half of the time trial. This strategy was also found to be practical to implement. In study 3, practical precooling and hyperhydration were evaluated to assess whether their combination offered further benefits to endurance cycling time trial performance, when assessed over the same laboroatory protocol. The main findings indicated that practical precooling and hyperhydration, with and without the co-ingestion of glycerol, failed to achieve a clear enhancement of cycling performance. However, when practical precooling and hyperhydration without glycerol was compared to the control condition (i.e., hyperhydration alone), there was a 2% (30 s) improvement in cycling performance time, which was detected in the second half (climb 2) of the time trial. These improvements may be partially explained by a lower percieved exertion, which was observed during the initial 10 km of the time trial.

Study 4 was conducted to validate anecdotal reports and laboratory-based observations of thermoregulatory strain in elite cyclists during a real-life event performed in temperate environmental conditions. The rationale for this study was to determine whether the magnitude of hyperthermia achieved during real-life cycling performed in temperate conditions was high enough to possibly benefit from precooling. Although fluid losses during racing were mild (1.3%), cyclists experienced hyperthermia, at magnitudes typically associated with heat-stress induced fatigue (>67% of observations). Therefore, in the final study of this thesis, the effects of practical precooling on 45.6 km cycling time trial performance was examined in both hot (32˚C) and temperate (21˚C) environmental conditions. The effectiveness of practical precooling was enhanced in temperate conditions, such that there was a greater magnitude of body cooling achieved. However, this strategy failed to provide a clear performance benefit in temperate conditions and instead, was likely to impair performance, particularly in the first (flat) section of the time trial course (-2.3%, 8 W).

Collectively, the studies contained within this thesis have contributed to the development of a practical precooling strategy involving the combined application of iced towels and ingestion of a slushie made from sports drink. These studies confirm the effectiveness of this novel strategy in reducing skin and core temperature and enhancing heat storage capacity prior to the commencement of exercise. However, the associated reduction in thermoregulatory strain translates into a performance enhancement in hot, but not temperate conditions. This thesis has provided detailed information regarding the range of factors that may be involved in altering the efficacy of a precooling manoeuvre and offers a highly practical insight into the application of precooling strategies aimed at improving field-based sports performance specific to time trial cycling.

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