Author(s): PALIN, T., SNAPE, D., WOODS, D., WAINWRIGHT, B., STACEY, M., OHARA, J., Institution: LEEDS BECKETT, Country: UNITED KINGDOM, Abstract-ID: 1968

INTRODUCTION:
Increasing hot weather and global temperatures place athletes and outdoor workers at increasing risk of Exertional Heat Illness (EHI). Heat Tolerance Assessment (HTA) has been used in surrogate for future EHI risk, in order to inform decisions on athletic return-to-play and occupational readiness, with protocols often attempting to dichotomise HTA outcomes as pass/fail. However, no international consensus exists in this area of preventative sports medicine. Furthermore, heat tolerance falls on a spectrum that may vary with individual factors including aerobic fitness and heat adaptation (acclimation or acclimatisation). In our experience, concerns arise for fitter individuals, who may pass HTA conducted at relative exercise intensity, but go on to suffer EHI with subsequent exercise-heat stress (i.e. false negative HTA result). We report data concerning metabolic responses to HTA tailored to individual factors in elite, well-trained and recreationally active athletes, and our progress towards better prognosticating EHI risk in the more highly trained.
METHODS:
Comprehensive observations of exercising heat tolerance in the elite class of athlete were made before and during a structured laboratory acclimation protocol. Results were used to construct HTA based on the work of Mee et al,(1) with an extension phase of the protocol tailored to lactate thresholds. Two groups of athlete were then recruited from well-trained (WT) and recreationally active (RA) groups. Each participant performed running HTA (30 min at LT1 followed immediately by 30 min at LT2, 1% gradient, 40°C and 40% relative humidity) on two days one week apart (HTA1 and HTA2), without intervening heat adaptation.
RESULTS:
Development of the HTA in elite running will be presented. As applied to WT and RA groups, HTA1 vs HTA2 showed no significant differences (P<0.05) at end exercise in core temperature (39.20 ± 0.44°C vs HTA2: 39.13 ± 0.46°C), skin temperature (38.83 ± 0.73°C vs. 38.44 ± 0.73°C), heart rate (181.20 ± 10.76 b·min-1 vs 178.00 ± 10.07 b·min-1), sweat rate (1.46 ± 0.48 kg·hour-1 vs1.25 ± 0.49 kg·hour-1), blood lactate (3.21 ± 1.41mmol·L-1 vs. 3.08 ± 1.34 mmol·L-1) or perceptual scores. Robust agreement between HTA1 and HTA2 was reflected in significant correlations and minimal participant variability on repeatability scoring. Nevertheless, the coefficient of variation was consistently lower for the WT group than the RA group, despite WT achieving significantly higher core body temperature than RA (WT: 39.50 ± 0.00, RA: 38.94 ± 0.42).
CONCLUSION:
Our results imply that the HTA is a reliable indicator of physiological and perceptual strain in hot conditions, with increased reliability in fitter individuals. Further work is required to understand its repeatability with heat acclimation and accuracy in predicting recovery from, and future susceptibility to, EHI.

1. Mee, J. A., Doust, J. and Maxwell, N. S. (2015) Repeatability of a running heat tolerance test. Journal of Thermal Biology, 49, pp. 91-97.