Potter, C., Hughes, D., Sharples, A., Davies, B., Dixon, N., Tuttle, J., Mauger, A., Castle, P., Chrismas, B., McNaughton, L, & Taylor, L. (2013). Combined effect of hyperhydration and pre-cooling on endurance cycling performance in hot and humid conditions. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 316.

This study determined if a 10-mile cycling time-trial performed in the heat could be improved by the combined strategies of hyperhydration and pre-cooling by reducing the negative thermoregulatory response to exercising in such an environment. Additionally, the cellular response, Hsp72 mRNA relative expression (Hsp72) was assessed pre- and post-exercise. Recreationally active males (N = 5) performed four 10-mile time-trials (30°C: 50% RH) on separate weeks with randomised conditions of hyperhydration, pre-cooling, both (hyperhydration plus pre-cooling), or a no-treatment control. Hyperhydration was administered through a glycerol solution and pre-cooling via cold water immersion (12 ± 2°C for 20 minutes). Glycerol or placebo was administered in all trials; with hyperhydration being determined by plasma volume levels through capillary blood sampling. Physiological measures of heart rate and blood lactate and thermoregulatory measures and core and skin temperatures were recorded throughout. Body mass and urine osmolality were monitored pre- and post-exercise. Venous blood samples were obtained at rest (pre- any intervention) and pre- and immediately post-exercise to assess HSP72 within leukocytes using qRT-PCR.

Pre-cooling performance time was significantly quicker by 6.1% than the control, 4.1% than hyperhydration, and 2.4% than pre-cooling + hyperhydration. Core temperature increase from pre- to post-10-mile time-trial was significantly less for pre-cooling and pre-cooling plus hyperhydration than the control and hyperhydration conditions. There was no significant difference between pre- and post-exercise Hsp72 levels across the four conditions.

Implication. Pre-cooling irrespective of the presence of hyperhydration elicited enhanced endurance performance in hot and humid environments.

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