How to Exercise Safely in High Humidity

During exercise, as the internal body heat rises, the body will naturally cool itself down by sweating. Particularly when it comes to high humidity during exercise, the cooling process is much more difficult to accomplish because sweat cannot evaporate off the body as easily as it does in less humid or dry conditions. Because of this, athletes often feel like they are exerting themselves much more than usual, but it is more likely that the conditions are draining their strength and changing (increasing) their rate of perceived exertion. McArdle, Katch, and Katch state, “Evaporation provides the major defense against overheating” and it is “Evaporation, not sweat, [which] cools the skin” (McArdle, et al., 2015). Therefore, if evaporation of sweat off the body is impaired due to the humid conditions, overheating and dehydrating are risks during moderate to intense sports practices or endurance exercises. This explains why most athletes would prefer hot, dry conditions to exercise in opposed to humid conditions even if the air temperature is lower. When high humidity is combined with high heat, this is when the weather can become dangerous to the athlete if they are not properly prepared or acclimated to the environmental conditions. Acclimating to the conditions includes, “Repeated exposure to hot environments when combined with physical activity improves exercise capacity, with less discomfort upon subsequent heat exposure” (McArdle et al., 2015). Interestingly, similar to acclimating to high altitudes, “...there is evidence that individuals living and training over many weeks in the heat might tolerate higher maximal core temperatures than those heat acclimated over 1 or 2 weeks” (Périard et al., 2015). Therefore, living and training in these climates is better; however, if moving is not a feasible option, acclimating can be done through training practices. 

Proper clothing is essential when it comes to exercising in high heat and humidity. “Warm-weather clothing should fit loosely to permit free circulation of air between the skin and environment to promote convection and evaporation from the skin. Moisture-wicking garments optimally transfer heat and moisture from the skin to the environment...” (McArdle et al., 2015) In addition, lighter colored clothing helps to reflect heat away from the body whereas darker colored clothing absorbs heat. Research done by Zhiwei Li and Yong Wang (2017) showed, “...professional sports clothing has good wicking ability [compared to cotton or polyester], and it can effectively reduce the surface temperature of the skin and the athletes sweat rate, which has a positive effect on athlete’s physiological responses” (Li & Wang, 2017). However, this light-weight, moisture-wicking clothing endurance athletes wear is much different compared to football players. Football players have many insulated layers with all of the padding and protective gear necessary for their sport. This insulation does not dissipate heat as easily and “effectively seal[s] off 50% of the body’s surface from the benefits of evaporative cooling” (McArdle et al., 2015). With athletes exercising in hot and humid environments, there are additional factors to take into consideration and acclimating to the heat and humidity is necessary, but it becomes extremely important to athletes like football players in these conditions.

The more an athlete of any kind physically exerts themselves, the hotter their core temperature will get. As stated, in high heat and humidity, it is hard for the body to cool itself through the evaporation of sweat itself since this function will be extremely limited. Acclimating to these adverse conditions is important. One way to do this is to overdress on less intense training days. The overdressing method is especially helpful for football players since they do not have options for reducing their layers at all as well as endurance runners if they have an event in a hot, humid, or tropical-like environment. This research suggests “...overdressing is a practical model for athletes seeking the benefits of exercise–heat acclimation while living and training in a temperate climate…” (Ely et al., 2018). The idea behind this is to prepare the body for the environmental conditions by slowly adding layers as the training weeks progress. This is meant to simulate the exertion level during an event and thereby acclimating the body to the hot, humid temperatures beforehand.

Another important consideration for exercising in hot, humid environments is proper hydration and replenishing electrolytes. This is important not only during exercise, but before and after to prepare the body and assist in a healthy recovery afterwards. A fascinating study took trained runners and evaluated their core temperatures during two separate moderate and intense runs with differing hydration levels in a hot environment. They found, “The dehydrated runners ran slower and at a lower intensity but reached a core body temperature that was higher than that of the same runner at a higher intensity but in a less dehydrated state” (Casa et al., 2010). The goal of proper hydration is to maintain plasma volume to allow circulation and sweat to progress as normally as possible to allow blood and oxygen to continue getting to the working muscles and to keep the athlete healthy throughout the practice, game, or run. Another study looked at the marathon distance in both a hot environment and a temperate environment for two consecutive years in Sao Paulo, Brazil. Water was allowed throughout the marathon, but certain electrolytes were only allowed on three occasions throughout the distance. Their findings showed, “...the marathon runner’s performance during the race was lower by approximately 13.5%, in accordance with the race time and race pace, in HE [hot environment] compared to TE [temperate environment]”. Although, “...in HE, we demonstrated more pronounced fluid and electrolyte imbalance…[and] loss of water and electrolytes can directly impact the performance and health” (Assunção Oliveira, R. et al., 2017). Further, “Maintaining a relatively high plasma sodium concentration by adding sodium to ingested fluid sustains the thirst drive, promotes retention of ingested fluids, and restores lost plasma volume more rapidly” (McArdle et al., 2015). All of this information proves the importance of hydration and electrolyte replenishment in adverse environmental conditions, but also proves that exercise can be done successfully despite the conditions.  

Finally, the last consideration would be to take breaks as necessary or to consider a slower pace during an endurance event. A slower pace during an endurance event may not be an ideal option for an elite athlete or one hoping for a certain qualifying time; however, overall health is important to take into consideration when environmental conditions are not optimal. During endurance events, Hannah Ellerton says, “...compare your overall pacing from previous runs...adjust by 2% to account for a temperature and heat index sum of more than 130. These same percentages apply to training” (Ellerton, 2019). Football players and other athletes playing intense sports cannot adjust pace so there are other strategies that can be used. In practice situations, the coaches are responsible for taking breaks as necessary. Also, during a game, if heat and humidity is a concern, there will be required “heat and humidity timeouts” for the safety of the players. Studies have shown that these breaks and timeouts can effectively reduce the stress on the athletes caused by the heat and humidity, especially when they are combined with cooling strategies. Some common strategies include setting up fans that the athletes can stand around when they aren’t playing, drinking cold/ice drinks, and cooling off with towels that have been soaked in ice water baths. Research has found, “...cold water/ice slurry ingestion is most favorable per[during]-cooling strategy. Vigorous cooling techniques that cover a large part of the body, or techniques that can be applied frequently, appear to be the best for improvement of exercise performance” (Bongers et al., 2017). Some strategies are more easily accessible and feasible to do before, during, and after practices or competitions, but coaches need to have plans in place for the health and safety of the athletes, especially in adverse conditions.  

When games, practices, or endurance events proceed as scheduled, it is important for coaches and athletes to know the signs and symptoms of heat-related illnesses before it is too late. Getting out before the peak temperatures hit as well as utilizing shaded areas as much as possible can help to mitigate the risks, but problems can still arise. Heat cramps, heat exhaustion, heat stroke, and exertional heat stroke are all problems that can come from exercising in high heat and humidity. Heat cramps are common among athletes, but can often be prevented by increasing fluid as well as salt intake prior to the intense practice, game, or event. As discussed, sweating disrupts the electrolyte balance and “Failure to replenish these minerals often leads to muscle pain and spasm…” (McArdle et al., 2015). Heat exhaustion is especially common when the athlete is not acclimated to the environment they are exercising in. This can happen during the first practice on an unusually warm or humid day (and proves the importance of endurance athletes acclimating themselves to the correct environment before they get to the location). In heat exhaustion, the plasma volume of the blood is reduced due to the increased sweat reaction caused by the temperature change and not being acclimated to it. This can result in a weak and rapid pulse, low blood pressure, headache, dizziness, weakness and decreased sweating as a bodily response to conserve as much fluid loss as possible. Heat exhaustion can be resolved by going to a cooler environment and replenishing with IV fluids (McArdle et al., 2015). Heat stroke is the most dangerous of these heat-related illnesses. “It reflects failure of the heat-regulating mechanisms from an excessively high core temperature and can affect seemingly healthy adults even in a relatively cool environment” (McArdle et al., 2015). Heat stroke generally presents as the core temperature exceeding 105° F, altered mental status, and complete absence of sweating. In addition, heat stroke always requires immediate medical attention otherwise it can certainly be fatal. Exertional heat stroke is similar to heat stroke, but is usually combined with intense activity and can often be treated with fluids, cold packs, or ice-water immersion. Interestingly, it also presents with a rapid breathing rate which “compensates for metabolic acidosis” (McArdle et al., 2015).         

Sarah Griffiths says, “...performing in hot climates can impair performance if the sporting individual is not adequately prepared for the environmental conditions…” (2019). Each of these methods, wearing light-weight, moisture-wicking clothing, hydrating and replenishing electrolytes, taking breaks or exercising at a slower pace or intensity, and acclimating to the environmental conditions have proven effective in being able to safely and healthily get through the practice, game, or event. However, in adverse conditions, it is also important for coaches and athletes to know and recognize the signs and symptoms of heat-related illnesses for the health and safety of the athletes. Therefore, while moderate to high intensity sports or endurance exercise may never get “easy” in hot and humid environments, there are ways that athletes can prepare and acclimate to the conditions as much as possible. 

References

Assunção Oliveira, R., Rennó Sierra, A., Benetti, M., Nabil Ghorayeb, N., Sierra, C., Augusta Peduti Dal Molin Kiss, M., & Fernanda Cury-Boaventura, M. (2017). Impact of hot environment on fluid and electrolyte imbalance, renal damage, hemolysis, and immune activation postmarathon. Oxidative Medicine and Cellular Longevity, vol. 2017, Article ID 9824192, 11 pages. doi: 10.1155/2017/9824192. Retrieved from: https://www.hindawi.com/journals/omcl/2017/9824192/ 

Bongers, C., Hopman, M., & Eijsvogels, T., (2017). Cooling interventions for athletes: An overview of effectiveness, physiological mechanisms, and practical considerations. Temperature (Austin, Tex.), 4(1), 60–78. doi:10.1080/23328940.2016.1277003. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5356217/  

Casa, D., Stearns, R., Lopez, R, Ganio, M., McDermott, B., Walker Yeargin, S., & Maresh, C., (2010). Influence of hydration on physiological function and performance during trail running in the heat. Journal of athletic training, 45(2), 147–156. doi:10.4085/1062-6050-45.2.147. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2838466/ 

Ellerton, H., (2019). Does running in heat and humidity affect athletic performance? Retrieved from: https://humankinetics.me/2019/02/19/running-in-heat-and-humidity/ 

Ely, B., Blanchard, L., Steele, J., Francisco, M., Cheuvront, S., & Minson, C., (2018). Physiological Responses to Overdressing and Exercise-Heat Stress in Trained Runners. Medicine & Science in Sports & Exercise, 50(6), 1285-1296. doi: 10.1249/MSS.0000000000001550. Retrieved from: https://journals.lww.com/acsm-msse/Fulltext/2018/06000/Physiological_Responses_to_Overdressing_and.20.aspx 

Griffiths, S., (2019). The effects of heat on sport performance. Retrieved from: https://believeperform.com/the-effects-of-heat-on-sport-performance/ 

Li, Z. & Wang, Y., (2017). Study on the effect of professional sports clothing on sports physiology. Biomedical Research 2018; Special Issue: S452-S457. doi: 10.4066/biomedicalresearch.29-16-1956. Retrieved from: https://pdfs.semanticscholar.org/2555/17b63b1c769a2173b61af91cd9e2ca763949.pdf    

McArdle, W., Katch, F., & Katch, V., (2015). Exercise Physiology: Nutrition, Energy, and Human Performance (8th ed.). Philadelphia, PA: Wolters Kluwer Health.

Périard, J., Racinais, S., & Sawka, M., (2015). Adaptations and mechanisms of human heat acclimation: Applications for competitive athletes and sports. Scandinavian Journal of Medicine & Science in Sports, 25(1), 20-38. doi: 10.1111/sms.12408. Retrieved from: https://onlinelibrary.wiley.com/doi/pdf/10.1111/sms.12408