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Blog: What is Heat Acclimation Training?

Heat acclimation training (HAT) is the artificial exposure to heat during exercise, for example exercising in a heated room or chamber. Training in the heat increases body (core and skin) temperature, induces profuse sweating and increases skin blood flow. All of these responses stimulate physiological adaptations, which improve an individual’s tolerance to exercise in the heat and reduce the chances of suffering from heat illnesses, such as heat exhaustion. HAT has been demonstrated to improve thermal comfort and aerobic exercise performance in warm-hot conditions (Costa et al., 2014; Willmott et al., 2016). Who does heat acclimation training? HAT is performed by individuals who wish to prepare for working or competing in warm-hot environments. HAT is routinely performed by athletes living in cold-moderate climates in order to prepare for an event in a warmer climate, for example Marathon Des Sables. There is limited evidence that HAT may improve athletic performance in moderate climates. A study in trained cyclists demonstrated a 6% improvement in time-trial performance in cool conditions following 10 days of HAT. However, the effectiveness of using HAT to improve performance in cool-moderate climates is not conclusive (Karlsen et al., 2015; Nybo et al., 2016). What does heat acclimation training involve? HAT involves performing endurance exercise (running, cycling etc.) for extended periods (45-60 minutes) at exercise intensities between 50-70% VO2max (Houmard et al., 1990; Cheung et al., 2000). Typically, the positive adaptations (see below) of HAT occur within the first 4-6 days. However, the rate at which the adaptations occur varies between individuals. For example, the adaptations occur faster in trained athletes (Taylor, 2014). Adaptations Heart rate and autonomic nervous system habituation which redirects blood flow to the skin and muscles. Thermal comfort Reduced perception of effort Earlier onset of sweating and á sweat rate Conservation of sodium chloride (salt) The benefits of HA are maintained for approximately 3 weeks (Garrett et al., 2011), with the potential for individuals to be able to spend up to 3-4 weeks in cooler conditions before the need to readapt (Weller et al., 2007). When should heat acclimation training be done? It is important HAT is undertaken close to the event to maximise the benefits. However, re-acclimatisation following an absence of HAT can occur relatively quickly (Porier et al., 2015). Author: Paul Hough (Sport/Exercise Scientist, St Mary’s University) Heat acclimation training is available at St Mary’s; please click here for more information, or for our latest special offers click here. References Cheung, S., McLellan, T., & Tenaglia, S. (2000). The Thermophysiology of uncompensable heat stress. physiological manipulations and individual characteristics. Sports Medicine, 29, 329-359. Costa, R., Crockford, M., Moore, J., & Walsh, N. (2014) Heat Acclimation Responses of an Ultra-Endurance Running Group Preparing for Hot Desert-Based Competition. European Journal of Sport Science, 14, 131-141. Garrett, A., Rehrer, N., & Patterson, M. (2011) Induction and Decay of Short-Term Heat Acclimation in Moderately and Highly Trained Athletes. Sports Medicine, 41, 757-771. Karlsen, A., Racinais, S., Jensen, M.V., Nørgaard, S.J., Bonne, T., & Nybo, L. (2015). Heat acclimatization does not improve VO2max or cycling performance in a cool climate in trained cyclists. Scandinavian Journal of Medicine & Science in Sports. 25, 269-76. Nybo, L. & Lundby, C. (2016), CrossTalk opposing view: Heat acclimatization does not improve exercise performance in a cool condition. Journal of Physiology, 594, 245–247. Poirier, M., Gagnon, D., Friesen, B., Hardcastle, S., & Kenny, G. (2015). Whole-Body Heat Exchange during Heat Acclimation and Its Decay. Medicine and Science in Sports and Exercise, 47, 390-400. Racinais, S., Buchheit, M., Bilsborough, J., et al. (2014). Physiological and performance responses to a training camp in the heat in professional Australian football players. International Journal of Sports Physiological Performance, 9, 598–603. Taylor, N., & Cotter, J. (2014). Heat Adaptation: Guidelines for the Optimisation of Human Performance. International Sportmed Journal, 7, 33-57. Weller, A., Linnane, D., Jonkman, A., & Daanen, H. (2007) Quantification of the Decay and Re-induction of Heat Acclimation in Dry-Heat following 12 and 26 days without Exposure to Heat Stress. European Journal of Applied Physiology, 102, 57-66. Willmott, A.G., Gibsona, O.R., Hayesa, B.M., & Maxwella, N.S. (2016). The effects of single versus twice daily short term heat acclimation on heat strain and 3000 m running performance in hot, humid conditions. Journal of Thermal Biology, 56, 59-67.

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