Morgan King MSc, RD
As we are in the full swing of summer it certainly brought heat and humidity (at least in Halifax, NS). Summer is the best time to do outdoor activities and sports. However, sports performance can be very affected by heat and humidity if you are not prepared. In particular, heat and humidity can greatly affect our core temperature resulting in dehydration and can lead to heat illness and in extreme cases heat stroke. Dehydration can happen very quickly if you do not keep up with it in the summer.
When it comes to heat and humidity, you will have an increased rate of sweat increasing fluid and electrolyte losses. The reason we sweat more is because our bodies' cooling system is trying to maintain an ideal core temperature. When we increase sweat, it is attempting to cool down our body by evaporation of water. The evaporation of the sweat is what ultimately cools us down.
Unfortunately, humidity makes cooling down more difficult because humidity increases the moisture particles in the air. When there are more water particles in the air, it messes with how sweat cools us down. When there is high moisture content in the air, our sweat does not evaporate as easily, instead, the sweat just rolls off the skin and leaves us in a puddle of sweat.
So how do we combat the adverse effect of heat and humidity? There have been a variety of studies comparing the differences between room temperature water, ice water, and slush (slurry) on thermoregulation (1,2) and more recently an International Olympic Committee (IOC) released a consensus on how to cool down while exercising (3,4) for the Tokyo 2020ne Olympics.
Here are some ways to cool down:
STRAIGHT-UP ICE WATER
Cold water was found to be effective in cooling down core temperature, thermal comfort, and performance compared to having room temperature water (1). If you are looking to cool down while exercising, having ice water is a perfectly reasonable way to go. As sweat increases, hydration needs increase, thus having ice water gives you the bonus of hydration and a cooling effect.
SLUSH (Slurries)
Interestingly, a study by Burton et al. (2013) monitored the effects of Slushies vs. Coldwater vs. room temperature water. From their findings they found slush was more effective in cooling core temperature down compared to room temperature water. In addition, Morris et al (2016) repeated a study on slush and found similar findings in there was a greater reduction in heat loss and concluded that ice slurries are effective in reducing core temperature. Moreover, it has also been the most effective to have before exercise or during exercise (3). As some of the studies described and re-reiterated by Juekendrup, consuming too much slush can increase gut distress, and reduce sweating which may not be optimal for sports that have high efficiency of sweat (i.e cycling, running, paddling etc..). Jeukendrup A. provides a great blog post on the pros and cons of slurries https://www.mysportscience.com/post/ice-slush-effects-benefits-and-evidence.
So, if you are looking to rapidly cool yourself down and you are in a sport in which sweating efficiency is less optimal because of gear, or not a heavy sweater. Slushy mixtures can be made with some blended ice with your choice of fruit juice, coffee, or electrolyte drinks (all depending on what you want it for). All you need is a blender that can crush ice and your preferred drink.
Water Mist Spray Bottles
Another way that you can cool yourself down during exercise is keeping using a mist spray bottle. Although these do help cool you down, you still will need to hydrate and replace the water losses and electrolytes you lose during exercise. Also depending on the environment mist bottles may not be as effective if the humidity is >70%. Mist bottles are more effective for cooling in lower humidity conditions (4).
Try out some or all of the ways and see what works best for you and adapt to the humidifying and heat environments. One cooling method may work more efficiently than the other depending on the circumstances.
References
1. Burdon CA, Hoon MW, Johnson NA, Chapman PG, O'Connor HT. The effect of ice slushy ingestion and mouthwash on thermoregulation and endurance performance in the heat. Int J Sport Nutr Exerc Metab. 2013 Oct;23(5):458-69. doi: 10.1123/ijsnem.23.5.458. Epub 2013 Mar 26. PMID: 23535809.
2. Morris NB, Coombs G, Jay O. Ice Slurry Ingestion Leads to a Lower Net Heat Loss during Exercise in the Heat. Med Sci Sports Exerc. 2016 Jan;48(1):114-22. doi: 10.1249/MSS.0000000000000746. PMID: 26258857.
3. S. Racinais, J. M. Alonso, A. J. Coutts, et al. J. D. Périard (2015). Consensus recommending on training and competing in the heat. Scand J Med Sci. 25; 6-19.
4. Racinais S, Hosokawa Y, Akama T, et al. IOC consensus statement on recommendations and regulations for sport events in the heat. British Journal of Sports Medicine 2023;57:8-25.
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