Effects of hot weather on the body

  • During exercise, muscle activity causes an increase in body heat.
  • To prevent an increase to the core temperature, the body responds with cooling mechanisms, such as shifting blood to the arteries closest to the skin, increasing the size of the blood vessels, and sweating. This allows for heat to be transferred or evaporated from the surface of the skin to the external environment.
  • As environmental temperatures and humidity increase, the cooling processes for heat transfer and evaporation becomes less effective. This can cause the body’s core temperature to increase.
  • In an effort to cool the body’s core temperature, the body will continue to increase the size of the blood vessels near the skin, and produce sweat to the skin, in hope heat will be transferred, and sweat will be evaporated from the skin and create a cooling effect. This can cause blood pressure to drop and increase heart rates. If cooling mechanisms are ineffective, internal temperature may continue to climb, and may cause you to experience dizziness, headaches or feel generally unwell. In extreme cases, this can cause heat stroke.

Heat safety guidelines

  • When considering exercising during warmer temperatures, consider using the Heat Safety Index. The Heat Safety Index refers to the “feels like” temperature, which includes humidity.
  • When the “feels-like” temperature is less than or equal to 28°C, it is safe for most people to follow their regular exercise prescription.
  • When the “feels-like” temperature is between 29°C to 38°C, it is recommended for most people to reduce your exercise prescription intensity and/or duration (time).
  • When the “feels-like” temperature is between 39°C to 45°C, it is recommended for most people to avoid exercising, and move exercise to an air-controlled cooler environment.
  • When the “feels-like” temperature is greater than or equal to 45°C, it is recommended for most people to completely limit exposure, and to move to an air-controlled cooler environment.

Precautions to take when exercising in the heat

  • Use the Heat Safety Index to determine if it is safe to exercise.
  • Consider air quality and smog when planning to exercise outdoors. Poor air quality can impair exercise tolerance and increase risk of experiencing symptoms.
  • If you have not been advised to limit your fluid intake by your doctor or healthcare provider, it is important to drink extra water (not caffeine or alcohol) during warmer climates to stay hydrated.
  • Consider changing the time of day you exercise.  Instead of exercising during peak heat hours (10 am to 3pm), try moving your exercise to early morning or late evening.
  • Wear light, breathable clothing and a hat. Exercise with training shoes, like running shoes, and avoid exercising in sandals or flip-flops.
  • Discuss the impact of your medications during warmer temperatures with your doctor or pharmacist.
  • Use sunscreen, especially over incision scar.

Indoor alternatives

  • There are several home-exercise videos you can complete from the comfort of your own home. If you do not have an air-controlled environment, consider exercising in a basement, or in the early morning or later evening. Try our warmup, resistance training with bands, resistance training with dumbbells or resistance training with body weight pre-recorded videos.
  • Consider indoor walking tracks with air control, indoor malls, large stores, or community centres.
  • Consider purchasing home exercise equipment, such as treadmills, stationary bikes, ellipticals or peddlers.

Want more information?

  • Speak to your Exercise Therapist.
  • Visit Air Quality Ontario for up-to-date information on air quality across Ontario www.airqualityontario.com
  • Call your local community centre(s) or mall(s) for information on indoor alternatives and hours of operation.