The impact of specific environmental conditions on training and competition performance is dependent on the nature of the thermal stress and the mode, duration and intensity of exercise. The effect of the environment contributes to the variation in human performance and can negatively impact physical work capacity of athletes. Moreover, quantifying the physiological and performance responses of athletes to varied environmental conditions during competition simulations and training provides important information for sport scientists and coaches to develop appropriate strategies to minimise sub-optimal performance. Whilst the effect of divergent environmental conditions on cycling and running performance have been well characterised, the effect on swimming performance is poorly defined. Mitigating detrimental effects of the environment on human performance may also be promoted using ergogenic aids. Per-cooling strategies, such as acetaminophen ingestion, have been proposed to reduce thermal strain during endurance sports such as Olympic distance triathlon, but the effect of acetaminophen has not been tested in trained endurance athletes. Therefore, the aims of the studies undertaken for this applied sport science thesis were to quantify the thermoregulatory and performance responses to (1) differing environmental conditions during training (swimming) and (2) acetaminophen ingestion under heat stress during endurance competition simulation (triathlon/cycling).
The first experimental study (Chapter 2) aimed to determine the effect of different environmental conditions on physiological and perceptual measures and training performance during outdoor swim training in elite and sub-elite swimmers. The hypothesis was that core and skin temperature and thermal sensation would be reduced during outdoor swimming in colder environmental conditions and would be associated with poorer training performance. Nine elite and ten sub-elite swimmers undertook outdoor swim training in a 50m heated pool in COOL (wet bulb globe temperature [WBGT] 14.7 ± 0.4 °C) and WARM (WBGT 23.0 ± 0.2 °C) or COLD (WBGT 10.3 ± 1.8 °C) and HOT (WBGT 27.0 ± 3.3 °C) environmental conditions, respectively. On each occasion matched training sessions were undertaken with a total swimming distance range of 5.6-6.9 km including three × 100 m efforts repeated 4 to 6 times completed by elite swimmers, whilst sub-elite swimmers completed 4.6-7.5 km with eight × 50 m sprints. Ambient temperature differed between COOL and WARM (ΔTa 7.9 °C, p < 0.001), and COLD and HOT (ΔTa 14.5 °C, p < 0.001). Skin temperature (Elite Δ Tsk 2.8 °C ± 0.5, d = 5.1; Sub-elite ΔTsk 4.5°C ± 1.0, d = 4.5; p < 0.001) and thermal sensation (Elite WARM: 4.6 ± 0.4 AU; COOL: 4.2 ± 0.8 AU, p = 0.006; Sub-Elite HOT: 4.8 ± 0.3 AU; COLD: 4.2 ± 0.6 AU, p = 0.028) were higher in WARM/HOT conditions compared to COOL/COLD but core temperature was not different. There were small improvements in swimming performance during WARM/HOT trials in elite and sub elite swimmers (Elite: 0.8-4.6%, d = 0.2-0.3; Sub-Elite: 2.3-4.8%, d = 0.3-0.6). Overall, skin temperature and thermal sensation vary dependent on ambient temperature during swimming despite consistent water temperature, with a small to moderate improvement in the quality of swim training during hot/warm compared to cold/cool seasonal conditions.
In the second experimental study, the aim was to determine the effect of acetaminophen (paracetamol) ingestion on physiological and perceptual measures during steady state cycling and time trial cycling performance of trained triathletes in hot and humid conditions. The hypothesis was that acetaminophen ingestion would decrease core temperature and thermal sensation and improve performance during an endurance cycling time-trial in the heat. In a randomised, double-blind crossover design, thirteen triathletes (4 female) completed ~60 min steady state cycling at 63% peak power output followed by a 7kJ·kg-1·BM-1 time trial in hot and humid conditions 90 minutes after consuming either a 20mg·kg-1·BM-1 dose acetaminophen (ACT) or a colour-matched placebo (PLA) (ACT, 29.9 ± 0.7 °C, 68.7 ± 2.7% relative humidity [RH]; PLA, 29.7 ± 0.7 °C, 68.7 ± 2.8% RH). In the ACT time trial, there was a moderate but not significant increase in time to completion (64.6 ± 112.7 s, d = 0.57, p = 0.086) and there was no difference in core temperature, skin temperature, thermal sensation, thermal comfort or fluid balance between conditions. Therefore, acetaminophen is not an effective ergogenic aid during endurance exercise in hot and humid conditions and existing heat mitigation strategies should be used during endurance competition.
In summary, the studies undertaken for this thesis provide novel information on the interaction between the thermoregulatory response and training, and competition performance in swimming and endurance cycling, respectively. Cold conditions appear to suppress sprint swimming performance and heat storage during endurance exercise in hot and humid conditions cannot be off set through acetaminophen ingestion. The studies in this thesis emphasise the importance of testing the effect of environmental conditions and ergogenic aids on the physiology and performance of athletes during exercise bouts with high external validity. Continued exploration of strategies that manipulate the thermal response to varied environmental conditions will assist sport scientists and coaches to optimise training and competition performance.