Should endurance athletes competing in the heat focus on cooling before or during competition?

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Stevens, C, Novak, A, Taylor, L, Callister, R, Dascombe, B 2016, 'Should endurance athletes competing in the heat focus on cooling before or during competition?', paper presented to Exercise & Sports Science Australia Conference: Research to Practice 2016, Melbourne, Vic., 14-16 April.


Introduction & Aims: A large research emphasis has been placed on cooling the body prior to exercise (pre-cooling) for the improvement of endurance performance in the heat. However, cooling during exercise (mid-exercise cooling) when the body is already under heat stress may be more beneficial. Therefore the purpose of this study was to compare the effect of practical pre-cooling and mid-exercise cooling methods on endurance running performance and physiology in the heat.

Methods: Eleven trained male runners (VO2max = 61±6 mL.kg-1.min-1) completed familiarisation and four randomised, pre-loaded running time trials (20 min at 70% VO2max followed by a 3 km time trial) on a non-motorised treadmill in the heat (33°C). Trials consisted of pre-cooling by combined cold-water immersion and ice slurry ingestion (PRE), mid-exercise cooling by combined facial water spray and menthol mouth rinse (MID), a combination of all methods (ALL) and a control (CON). A range of physiological responses was measured throughout the trials.

Results: Performance time was significantly faster in MID (13.7±1.2 min; P<0.01) and ALL (13.7±1.4 min; P=0.04) but not PRE (13.9±1.4 min; P=0.24) compared to CON (14.2±1.2 min). Pre-cooling significantly reduced rectal temperature (initially by 0.5±0.2°C), mean skin temperature, heart rate and sweat rate and increased iEMG activity. Mid-cooling increased expired air volume and respiratory exchange ratio. Decreases in forehead temperature, thermal sensation and post-exercise blood prolactin concentration were observed in each condition.

Conclusion: Running performance was improved by equal magnitude in both MID and ALL while PRE had little or no influence, despite reducing markers of cardiovascular strain and increasing iEMG activity. Hence, endurance athletes should focus on cooling during exercise. Mid-exercise cooling may have improved performance through an attenuated inhibitory psychophysiological and endocrine response to the heat