Strategies to mitigate the effects of heat in high temperature climates and improve performance

      Here in Austin, TX where we live, train, and spend over 50% of our competitive season, we know a thing or two about BBQ meats, music in the streets, and living in the heat. The MLS regular season in its current format runs from February until early November, that means a significant portion of that time is during the hottest parts of the year. According to the National Weather Service, in Austin the average temperature on any given day during the months of May through August in the last decade was 77.3 to 87.1 °F, with average daily high temperatures of 94.9 to 104.5 °F1. Heat can be an important environmental factor affecting both athlete performance and overall wellness. As practitioners within professional sports where athlete performance and readiness/availability are key, it’s paramount that we take such a significant environmental factor into account when planning event management, athlete preparation, and athlete recovery post exercise. 

      Given that once the ambient air temperature is over 68 °F 98% of body cooling is done through evaporation of sweat2 and if relative humidity is high sweat cannot evaporate2, we must also take that factor into account. Wet Bulb Globe Temperature (WBGT) is measured as part of a formula that uses a relationship between ambient air temperature in direct sunlight, a wet thermometer’s air temperature, and a shaded thermometer’s air temperature, and is the main measurement used for interpreting the severity of heat and humidity on athletes2. With this in mind, the MLS policy is that if the WBGT is above 82 °F mandatory hydration breaks will be implemented during each half of the game as well as at the referee’s discretion for player safety4. The average relative humidity in Austin during these months listed earlier is 67.5%5. Now as mentioned more goes into just WBGT than only ambient air temperature and relative humidity, but an estimate from the University of Connecticut would place numbers like that at WBGTs of 78.8 to 91.4 °F6. 

      Exercise, especially high intensity prolonged exercise like soccer, in that type of environment not only affects performance in the moment2,3, but also recovery post exercise7,8.  For training and games we’ll make sure to have tools such as ice towels, cooling vests, ice slurries/slushies, cold tubs, and cryotherapy chambers available for use. Each of these can help with athlete performance and cooling in different ways, and using a mix of them allows us to get the most efficient benefits to performance and recovery3. 

      We keep cooling vests available before and during games for our athletes to wear during and after warmups, and at halftime. Cooling vests have been shown to be effective in pre-match capacities because they can lower skin temperature without reducing muscle temperature. This allows athletes to cool themselves without sacrificing the warm up that you’ve already done3. The limitation of ice vests is that they really only affect skin temperature, and generally the cooling effect can’t actually directly affect the core body tissue and organs to create overall body cooling3. 

      Ice slurries/slushies can be an efficient way to pre-cool the core of the body as well without effecting muscle temperature. Because of the increased energy needed to phase change ice to a liquid, ice slurries have been shown to be more beneficial than just cold drinks in cooling3. We have a machine to make slushies out of our isotonic drinks so that athletes can get the benefit of having those and the cooling effects. But having a machine on site can be expensive, and you have to be aware to use a drink with the correct proportion of sugar to freeze into a slushie. Also some studies have shown that while slushies can be good at increasing perception of cooling in the athlete, it would be hard to drink enough to actually create a direct improvement on performance10. 

      For during the game on the sidelines and at practice we keep ice towels in ice water in a cooler. Working through a similar method as the cooling vests to cool athletes3, these are easier to take on and off and more practical to store and transport on the sideline and on the field which is why we use them then. During training we move their location to be between drills so that as athletes are moving from one drill to the next or listening to coaches talk they can put these over their heads/necks and help themselves cool down before playing again. In games with hydration breaks we have these ready on the sideline so athletes can quickly get them on and off in a short period of time.  

      Cold Water Immersion can be a great recovery tool. We have a tub at our training facility that athletes can access whenever they like. When used post training or exercise, CWI immediately post exercise has been shown to increase central nervous system recovery, maximal voluntary muscular contraction, and motor unit recruitment within 24 hours8. Usually our athletes will go into the tubs for ten to fifteen minutes at a time, but some research has shown that going in for as long as 30 minutes at a time can be beneficial3. The difficulty of cold tubs is that they can be time intensive to set up, and once they are set up they are not moveable. At our training facility we have an automated cold tub built into floor of our facility, but at games we fill large rubber tubs with ice and water to have a cold tub available. 

      Also in our training center we have a cryotherapy chamber that is kept at -150 °F. Whole body cryotherapy has shown a number of benefits for athletes. When used post exercise it has been shown to increase testosterone levels for 24 hours leading to decreased inflammation, improved sleep quality, and increased motivation for subsequent workouts in later days. This can be especially useful to us given the possibility of having weeks with multiple games played in a short period of time9. Because of the extreme cold temperatures the chamber keeps itself at, we have a strict three and a half minute limit on the amount of time anybody can be in the machine, and the machine has an alarm that will sound as soon as somebody has been in there for their allotted time. Even recognizing the absolute benefits of a treatment such as this, the cost can be prohibitive, with new units costing over $40,000 a lot most of the time and high end units costing over $60,00011. 

      These are the strategies that we have implemented and had success with. No matter which of these approaches you choose to use, the important part is to think about the how and why of what you’re doing. As athletic trainers it is our job to make sure we are making the most informed and best decisions with a rational base behind them so that athletes will buy in and make the most of the resources we provide for them. 

Scott Bohrer 

Assistant Athletic Trainer 

Austin FC 

sbohrer@austinfc.com 

References 

1. US Department of Commerce NOAA. Climate History. https://www.weather.gov/wrh/Climate?wfo=ewx. Published March 3, 2022. Accessed July 14, 2022. 
2. Coris EE, Ramirez AM, Van Durme DJ. Heat illness in athletes: the dangerous combination of heat, humidity and exercise. Sports Med. 2004;34(1):9-16. doi:10.2165/00007256-200434010-00002 
3. Racinais S, Alonso JM, Coutts AJ, et al. Consensus recommendations on training and competing in the heat. Br J Sports Med. 2015;49(18):1164-1173. doi:10.1136/bjsports-2015-094915 
4. Competition Guidelines. Major League Soccer. https://www.mlssoccer.com/about/competitionguidelines#:~:text=Each%20cooling%20break%20will%20last,and%2075th%20minute%2C%20respectively). Accessed July 14, 2022.  
5. Austin, TX - climate & monthly weather forecast. Weather U.S. https://www.weather-us.com/en/texas-usa/austin-climate#humidity_relative. Accessed July 15, 2022. 
6. Belval L. Wet Bulb Globe Temperature Monitoring. Korey Stringer Institute. https://ksi.uconn.edu/prevention/wet-bulb-globe-temperature-monitoring/#. Published March 5, 2015. Accessed July 15, 2022.  
7. Donnan K, Williams EL, Stanger N. The Effects of Heat Exposure During Intermittent Exercise on Physical and Cognitive Performance Among Team Sport Athletes. Percept Mot Skills. 2021;128(1):439-466. doi:10.1177/0031512520966522 
8. Minett GM, Duffield R, Billaut F, Cannon J, Portus MR, Marino FE. Cold-water immersion decreases cerebral oxygenation but improves recovery after intermittent-sprint exercise in the heat. Scand J Med Sci Sports. 2014;24(4):656-666. doi:10.1111/sms.12060 
9. Russell M, Birch J, Love T, et al. The Effects of a Single Whole-Body Cryotherapy Exposure on Physiological, Performance, and Perceptual Responses of Professional Academy Soccer Players After Repeated Sprint Exercise. J Strength Cond Res. 2017;31(2):415-421. doi:10.1519/JSC.0000000000001505 
10. Choo HC, Peiffer JJ, Lopes-Silva JP, et al. Effect of ice slushy ingestion and cold water immersion on thermoregulatory behavior. PLoS One. 2019;14(2):e0212966. Published 2019 Feb 27. doi:10.1371/journal.pone.0212966 
11. Bakke, M. How Much Does a Cryotherapy Chamber Cost? Cryotherapy Innovations. June 22, 2020. Accessed July 23, 2022. https://www.cryoinnovations.com/blog/2020/6/22/baqh7nuazudtozkj1wggwqj3jkgvj5#.Yt6uduzMI-Q