The purpose of this thesis was to optimise preparation for endurance runners competing in a hot environment. A multidisciplinary approach was adopted, investigating acute and chronic interventions to identify the most effective preparation. The determinants of endurance performance model (Bassett & Howley 2000) facilitated simultaneous investigation of the efficacy of interventions as well as the physiological mechanisms through which interventions influence performance. Finally, a retrospective analysis was conducted to identify the relationship between physiological markers and endurance running in the heat, in order to inform training prioritisation.
Study 1 investigated the validity and reliability of skin temperature (TSKIN) measurement tools at rest and during treadmill running, to identify an appropriate measurement tool for use in subsequent studies, without restrictive trailing wires. A thermal camera provided insufficient levels of validity and reliability for safe monitoring of TSKIN, while telemetry thermistors provided a viable and more convenient alternative to the criterion measure of hard-wired thermistors.
Study 2 investigated the effect of evidenced and practical internal (eg. ice slurry ingestion) and external precooling (eg. ice packs, forearm immersion and cold garments) strategies during incremental running in the heat. No differences were observed across the determinants of endurance performance between cooling techniques, with both eliciting modest reductions in blood lactate accumulation, compared with no cooling, which may prevent a decrement in the lactate turnpoint speed under heat stress. However, external cooling elicited a greater reduction in TSKIN and thermal sensation, alleviating perceived thermal strain further than internal cooling.
Study 3 investigated ischaemic preconditioning (IP), which may enhance endurance performance through haemodynamic and/or metabolic mechanisms, prior to incremental running in the heat. IP had no effect on the determinants of endurance performance. The thermoregulatory responses to exercise-induced hyperthermia may supersede previously reported effects of IP, which is not recommended as an ergogen prior to exercise in the heat.
Study 4 investigated the effect of a chronic strategy, involving five days of controlled hyperthermia heat acclimation (HA), on the determinants of endurance performance and a 5 km time trial in the heat. Heat acclimation improved V̇O2max, the lactate thresholds and 5 km performance. Alleviated physiological, thermal and metabolic strain were observed, likely attributable to enhanced cardiovascular stability and heat dissipation. Five days of controlled hyperthermia HA appears to be a potent strategy to support endurance running in the heat.
Study 5 directly compared acute (external precooling), chronic (HA) and combined (precooling & HA) strategies during 5 km running. Precooling did not improve performance following HA, despite modest alleviation of physiological strain, which may indicate an inappropriate pacing strategy. Heat acclimation improved performance further than precooling (HA +6.6%, precooling +3.7%), indicating HA should be prioritised, although precooling appears beneficial when acclimation is not possible.
Multiple, linear regression indicated the physiological determinants of endurance performance do not accurately predict endurance performance in the heat (R2=0.72, standard error of the estimate =105.6 s). The unexplained variation during endurance performance in the heat may reflect a greater prominence of perceptual measures to influence running in the
heat. Preparation for competition in the heat should therefore prioritise improving perceived thermal and exertional strain under heat stress, alongside improving traditional physiological markers.