Running in Hot Weather

By: Ryan Hudson, MD

It looks like the hot weather just might be here to stay after a very cool May and first part of June. As your body adjusts to the climate, here are some tips from Dr. Ryan Hudson from the University of Chicago Medicine’ s Orthopaedics Center.

When exercising in hot weather, it is important to be mindful of the impact the heat can have. One way to determine the level of heat risk is the “Wet Bulb Global Thermometer,” index, or WBGT. It measures air temperature, humidity and radiant heat (sunlight). Higher WBGT temps mean harsher conditions. If the WBGT is greater than 75, there is a higher likelihood that the conditions will impact your performance. When the level is over 90, activity should be restricted.

Heat associated conditions can range in severity from heat cramps through heat exhaustion to heat stroke. Heat exhaustion is a general term used to describe a series of symptoms associated with elevated body core temperature that includes headache, fatigue, weakness, dizziness, cramps, nausea, vomiting and diarrhea. Heat stroke is much more serious but also a very rare situation believed to be caused by a loss of thermoregulatory control. Symptoms are the same as heat exhaustion, but with added changes in mental status - delirium, seizures and even coma in the worst cases. The exact causes of heat stroke are not that well understood, and thankfully it is a relatively rare event that most of us will never experience even in the hottest conditions.

Generally, humans are well equipped physiologically to regulate their body temperatures in all except in the most extreme environmental conditions. Still, we should be mindful of the heat and understand how it can affect us. Given that summer and hotter temps are probably here to stay until the autumn, here are some broad strategies that can help:

  1. Hydration – Exercising in hot temperatures while in a dehydrated state can compromise performance and put you at risk. Consuming a normal mixed diet typically results in healthy hydration levels. Be aware of situations in which you might deviate from your routine, such as long travel or other unusual circumstances where you might not eat and drink regularly.

    Humans are not camels, so we cannot store water. Drinking in excess will just mean you produce more urine. Sweat rates can vary widely between individuals, but drinking to thirst will ensure you get the right amount for you. Typically this is between 12-32 fl oz each hour.

  2. Clothing – Wear light colored, light weight and permeable clothing with sun protection. If you must be out in the peak hours of the day, be aware of sun burn, and consider wearing a hat to keep the sun off your face.

  3. Medication – Some medications or over-the-counter products contain substances that could affect your ability to regulate your temperature. Be aware if you are currently taking any medication that contains antihistamines, or stimulants.

  4. Activity planning/reduction – Exercise performance worsens as the temperature rises, so it helps to make sure your expectations are appropriate. Expect to go a little slower than normal, and it’s probably best not to try for a personal best performance in the heat.

  5. Acclimatization to elevated temperatures – It can take 7-10 days of exposure to warmer temperatures for the body to make the requisite adaptations which result in improved thermoregulation. Be mindful of sudden increases in temperature at home, or of much warmer and humid conditions if you travel to an event, and set the right expectations as per #4 above.