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  • Writer's pictureLyns Romano

Running in Hot/Warm Conditions: Key Considerations for Distance Runners



Whether racing, training, or simply heading out on an easy daily run, understanding the impact of heat and humidity on your body and making necessary adjustments can help you get the most from your training this summer. This article examines the physiological effects of running in hot weather and actionable advice for modifying your training. Further, we'll underscore hydration's critical role, and investigate the unanticipated benefits of acclimatizing to high temperatures.


When running in warm conditions, our body temperature rises, prompting physiological responses to prevent overheating. The primary cooling mechanism is sweating, which lowers the skin's surface temperature as sweat evaporates. Additionally, increased blood flow is directed to the skin to aid cooling, reducing the blood available for muscles and organs. This shift can lead to higher effort or reduced performance for the same workload (Cheuvront et al., 2010).


Training Adjustments for Warm Weather

As distance runners, maintaining the same pace or distance in hot weather demands more effort than in cooler conditions. To manage this, it's essential to adjust either speed, distance, or a combination of both to prevent overexertion.


Training/Racing Pace

Adjusting the pace is crucial when training distances remain unchanged. The degree of adjustment depends on temperature, humidity, and acclimatization levels.


Using Dew Point for Adjustments: Dew point, which measures air saturation, is the best indicator for determining warm weather pace adjustments. Here's how to use it:

  1. Combine air temperature and dew point using the below chart from Maximum Performance Running:


2. Use the value to adjust your pace:


  • 100 or less - no pace adjustment

  • 101 to 110 - 0% to 0.5% pace adjustment

  • 111 to 120 - 0.5% to 1.0% pace adjustment

  • 121 to 130 - 1.0% to 2.0% pace adjustment

  • 131 to 140 - 2.0% to 3.0% pace adjustment

  • 141 to 150 - 3.0% to 4.5% pace adjustment

  • 151 to 160 - 4.5% to 6.0% pace adjustment

  • 161 to 170 - 6.0% to 8.0% pace adjustment

  • 171 to 180 - 8.0% to 10.0% pace adjustment

  • Above 180 - Hard running not recommended


Notes:


  1. The ranges account for individual factors such as fitness level, physical make-up, and acclimatization to heat and humidity.

  2. For interval training, reduce the pace adjustment by roughly half since recovery periods allow the body to cool down between efforts (Maughan et al., 2010).


Hydration

Effective cooling through sweating requires adequate hydration. Maintain good hydration habits throughout the day, intra-run, and, rehydrate well after runs. For runs over 40 minutes in warm weather, consider taking fluids during the run, and possibly some electrolytes during longer sessions (Sawka et al., 2007).


Positive Effects of Heat Training

Training in the heat can offer benefits similar to altitude training. Both conditions reduce oxygen delivery to muscles and organs, prompting the body to increase blood supply. This adaptation can enhance performance (Periard et al., 2015). Additionally, heat training improves the body's efficiency in cooling itself, which benefits performance in cooler conditions (Nybo et al., 2014).


Heat Acclimation

Heat can decrease VO2max, but proper heat acclimation can mitigate some of this impact. It typically takes around two weeks to acclimate, with significant adaptations occurring within the first 5-9 days and nearly full adaptations by 8-10 days (Garrett et al., 2011). After this period, maintain your heat adaptations with exposure every three days.


By understanding and adjusting for the effects of heat on the body, you can optimize your training and performance, even in challenging weather conditions.


The Danger of Heat and Heat-Related Illness


Running in hot conditions can significantly increase the risk of heat-related illnesses, which range from mild to life-threatening. Knowing the signs and symptoms of heat illness is crucial.


Heat Cramps and Syncope: Heat cramps typically occur in the muscles used during exercise, such as the calves, thighs, and shoulders. They are often accompanied by heavy sweating and muscle pain. Heat syncope, on the other hand, involves a temporary loss of consciousness due to the body's attempt to redirect blood flow to the skin to aid cooling, which reduces blood flow to the brain.


Heat Exhaustion: Heat exhaustion is a more serious condition that can occur after prolonged exposure to high temperatures, particularly when combined with high humidity and strenuous physical activity. Symptoms include heavy sweating, paleness, muscle cramps, tiredness, weakness, dizziness, headache, nausea or vomiting, and fainting. If untreated, heat exhaustion can lead to heat stroke.


Heat Stroke: Heat stroke is the most severe heat-related illness and a medical emergency. It occurs when the body is unable to regulate its temperature, which rises rapidly to dangerous levels. Symptoms include a high body temperature (above 104°F), hot and dry skin, rapid pulse, confusion, seizures, and loss of consciousness. Immediate medical attention is crucial to prevent organ damage or death.



References:

  • Cheuvront, S. N., Ely, B. R., Kenefick, R. W., & Sawka, M. N. (2010). Biological variation and diagnostic accuracy of dehydration assessment markers. The American Journal of Clinical Nutrition, 92(3), 565-573.

  • Garrett, A. T., Creasy, R., Rehrer, N. J., Patterson, M. J., & Cotter, J. D. (2011). Effectiveness of short-term heat acclimation for highly trained athletes. European Journal of Applied Physiology, 111, 1477-1485.

  • Maughan, R. J., Shirreffs, S. M., & Watson, P. (2010). Exercise, heat, hydration and the brain. Journal of the American College of Nutrition, 29(sup3), 267S-274S.

  • Nybo, L., Rasmussen, P., & Sawka, M. N. (2014). Performance in the heat—physiological factors of importance for hyperthermia-induced fatigue. Comprehensive Physiology, 4(2), 657-689.

  • Periard, J. D., Caillaud, C., & Thompson, M. W. (2015). The role of aerobic fitness and exercise intensity on endurance performance in uncompensable heat stress conditions. European Journal of Applied Physiology, 115(5), 837-847.

  • Sawka, M. N., Cheuvront, S. N., & Carter, R. (2007). Human water needs. Nutrition Reviews, 63(suppl_1), S30-S39.

  • American Academy of Orthopaedic Surgeons. (2024). Heat Injury and Heat Exhaustion. Retrieved from https://orthoinfo.aaos.org/en/diseases--conditions/heat-injury-and-heat-exhaustion/

  • Casa, D. J., Armstrong, L. E., Hillman, S. K., Montain, S. J., Reiff, R. V., Rich, B. S. E., ... & Stone, J. A. (2000). National athletic trainers' association position statement: fluid replacement for athletes. Journal of Athletic Training, 35(2), 212.

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