Effect of precooling and acclimation on repeat-sprint performance in heat in males

[Truncated abstract] Precooling is an acute method of cooling the body prior to exercise. It is used principally in an attempt to lower core temperature, thus increasing the time taken to reach a critical thermal maximum during exercise, at which a given intensity can no longer be maintained. To date, most research has focused on the effects of precooling on endurance exercise, with results consistently showing performance benefits. Currently, only limited research is available on the effects of precooling on repeat-sprint exercise, which is surprising as these demands form a major component of team-sport performance. Notably, many precooling methods used in previous research are not practical to an actual field situation, i.e., cold water immersion and the use of climate chambers. Consequently, the main objective of this thesis was to investigate practical methods of precooling that involved internal and external techniques alone or in combination (i.e., ice slushy ingestion and/or cooling jacket) on repeat-sprint performance in heat, in both a laboratory situation, as well as an outdoor setting. This thesis also explored the use of precooling in conjunction with heat acclimation/acclimatisation, as this area has not been previously well researched. Study one, the first of three experimental studies, evaluated the effects of different precooling procedures on prolonged repeat-sprint cycling exercise (2 x 30-min halves comprising 30 x 4 s maximal sprints interspersed with sub-maximal intensity exercise) in heat (~35°C and 60% relative humidity). This study aimed to determine whether internal (ice slushy) or external (cooling jacket) precooling methods would provide any benefit to repeat-sprint exercise performance and whether any improvement would be greater using these methods simultaneously. The most effective precooling method would then be used in both subsequent studies. Study two aimed to investigate the effect of partial heat acclimation (5 sessions of cycling at 80% maximum power output for 3-min with 1-min passive rest, for 32 to 48 min) on repeat-sprint performance (as in study one) in heat and to determine whether any further benefits would occur with the addition of precooling performed both prior to and during exercise. Study three assessed the effects of precooling used prior to and during an outdoor simulated running team-sport game (4 x 20-min quarters with 2 x 5-min quarter and 1 x 10-min half-time break) on seasonally heat acclimatised individuals...