Exercising when it’s warm

I am susceptible to heat illness and (unfortunately) I am still learning that it isn’t as straight-forward to manage as going out early/late in the day and drinking enough water.

A couple of weeks ago I went out intending to do a long, slow distance run early in the morning (about 7am). It was about 19C when I started out and the final temp, almost 2 hours later, was in the low 20s. Although I thought the temperature was perfect, I became mildly dehydrated after about 90 minutes from the strong wind and direct sun. I was also feeling a false sense of security because of the relatively low temperatures—I wasn’t drinking as much water during the run as I normally would have in higher temperatures.

So learn from my mistakes and consider these other points before you go out and do any kind of exercise this summer:

Intensity– the greater the intensity of exercise the more heat you generate. So the warmer and more humid the weather is the more you need to slow down or decrease intensity.

Body mass– the bigger you are the more heat your body generates and the more ‘insulation’ you have. You really don’t want a lot of insulation in hot weather.

Medication– antihistamines, anti-depressants, anti-inflammatories, blood pressure medications and many other meds can interfere with your body’s heat balance system.

Caffeine– drinking coffee, tea, or other caffeinated drinks before warm weather exercise can cause you to generate more heat and experience an increased heart rate.

Sweat evaporation– sweating doesn’t cause heat loss–it is the evaporation of sweat that causes it. The higher the humidity the less sweat evaporates.

Air temperature– your body generates a lot of heat during exercise so it makes sense that if the surrounding air and objects are cooler, it’s going to be easier to dissipate the heat.

Clothing– lighter colours reflect the sun’s rays so during warmer weather avoid dark clothing. Clothing also traps air next to your skin, which will then heat to body temperature and act as an insulator. This is especially true of non-porous or tight fitting clothing. The best thing to do is wear light, breathable gear. Cotton t-shirts are the absolute worst thing to wear for exercising in warm weather… they just absorb sweat and hold onto it.

Hats– we dissipate a substantial amount of heat through our heads. Stick to mesh running caps that allow the heat to escape.

Below are some common heat-related illnesses, their causes and symptoms.

Heat cramps

Cause: electrolyte deficiency or imbalance due to exercising in hot weather.

Symptoms: sharp, stabbing pain in muscles, especially leg muscles; although they can occur in the diaphragm, resulting in very painful side stitches.

What to do: stop running/exercising, try to drink fluids containing electrolytes, cool the body with wet towels or whatever is at hand and get to a cool area immediately. Get medical attention if necessary.

Heat exhaustion

Cause: body is unable to dissipate enough heat generated during exercise in warm, humid conditions and also loss of electrolytes.

Symptoms: moderate rise in body temperature, dizziness, nausea, vomiting, headache, weakness, lack of coordination, heat cramps, heavy sweating accompanied by moist and cold skin, ‘goose bumps’, rise in heart rate, fatigue that causes you to slow down.

What to do: stop exercising, drink fluids containing electrolytes, cool the body/get to a cool area immediately, lie down with feet elevated a few inches above the heart. Getting prompt medical attention is also highly recommended. Untreated heat exhaustion can rapidly progress to heatstroke.


Cause: body’s thermoregulation fails. It cannot dissipate the heat generated during exercise and core body temperature rises to a dangerous level. Untreated heat exhaustion can rapidly progress to heatstroke.

Symptoms: may or may not include symptoms of heat exhaustion. Symptoms include lethargy, extreme weakness, confusion, odd behaviour, disorientation, unconsciousness, cessation of sweating, hot, dry skin. Can lead to convulsions, seizures, coma, and death.

Treatment: This is a medical emergency that requires immediate medical attention. Move person to a cool area, and try to cool their body with ice or cold water.

Please be careful out there!