Conductive and evaporative precooling lowers mean skin temperature and improves time trial performance in the heat S. H. Faulkner 1,2 , M. Hupperets 3 , S. G. Hodder 1 , G Havenith 1 1 Environmental Ergonomics Research Centre, Loughborough Design School, Loughborough University, Loughborough, UK, 2 National Centre for Sport and Exercise Medicine, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK, 3 ait Sport Research Laboratory, Adidas AG, Herzogenaurach, Germany Corresponding author: George Havenith, PhD, Environmental Ergonomics Research Centre, Loughborough Design School, Loughborough University, LE11 3TU,UK. Tel: +44 (0)1509 228485, Fax: +44 (0)1509 226900, E-mail: G.Havenith@lboro.ac.uk Accepted for publication 19 October 2014 Self-paced endurance performance is compromised by moderate-to-high ambient temperatures that are evident in many competitive settings. It has become common place to implement precooling prior to competition in an attempt to alleviate perceived thermal load and perfor- mance decline. The present study aimed to investigate precooling incorporating different cooling avenues via either evaporative cooling alone or in combination with conductive cooling on cycling time trial performance. Ten trained male cyclists completed a time trial on three occa- sions in hot (35 °C) ambient conditions with the cooling garment prepared by (a) immersion in water (COOL, evaporative); (b) immersion in water and frozen (COLD, evaporative and conductive); or (c) no precooling (CONT). COLD improved time trial performance by 5.8% and 2.6% vs CONT and COOL, respectively (both P < 0.05). Power output was 4.5% higher for COLD vs CONT (P < 0.05). Mean skin temperature was lower at the onset of the time trial following COLD compared with COOL and CONT (both P < 0.05) and lasted for the first 20% of the time trial. Thermal sensation was perceived cooler following COOL and COLD. The combination of evaporative and conductive cooling (COLD) had the greatest benefit to performance, which is suggested to be driven by reduced skin temperature following cooling. Introduction Endurance exercise performance progressively deterio- rates as the surrounding ambient temperature increases (Galloway & Maughan, 1997), which is further exacer- bated when combined with increasing humidity (Watson et al., 2011). It appears that there is a strong link between increases in thermoregulatory strain, due to elevations in both metabolic and ambient heat, and impaired endur- ance performance. The attainment of a critical core body temperature of approximately 40 °C has been proposed as the main factor limiting endurance performance in hot environments (Gonzalez-Alonso et al., 1999). It is sug- gested that this critical core temperature (T c ) is used as a set point, around which the body bases pace judgment alteration and effort perception in an attempt to complete a given task as quickly as possible without achieving a dangerously high core temperature (Marino, 2004; Schlader et al., 2011a). However, recent work on self- paced exercise indicates that a T c of > 40 °C may not be critical in performance determination (Ely et al., 2009), particularly when considering self-paced rather than fixed intensity exercise. Increases in skin temperature in response to exercise have been suggested to be an important factor in regu- lating endurance performance in warm ambient condi- tions (Kenefick et al., 2010; Sawka et al., 2012). In hot conditions, fatigue has been shown to be less reliant on high absolute core temperature, but more dependent on hot skin temperature (> 35 °C), as fatigue occurred at relatively low core temperatures of approximately 38.5 °C (Latzka et al., 1998; Montain et al., 1994). Ways to alleviate the deleterious effect excessive thermal strain has on performance have received wide- ranging focus. One of the most widely adopted practices is that of precooling. Precooling can be applied exter- nally using a variety of methods (Kay et al., 1999; Bogerd et al., 2010), internally via the use of cold or ice slurry beverages (Ross et al., 2013), or via combinations of precooling methods (Ross et al., 2011). All of these have the aim of reducing core temperature prior to the onset of exercise, thereby increasing the body’s ability to store endogenous and exogenous heat and consequently improving exercise performance (Ross et al., 2013). Several previous studies have demonstrated that pre- cooling prior to exercise has a beneficial effect on perfor- mance (for a review see Tyler etal., 2015). However, few studies consider ways in which precooling may be influ- enced by the type of cooling (e.g., evaporative, conductive, convective) and the effect this may have on performance. Scand J Med Sci Sports 2015: 25 (Suppl. 1): 183–189 doi: 10.1111/sms.12373 © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd 183