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Healtheuniversity > English > Diabetes College > Get Active > Safe Exercise > Exercise in Hot Weather

Exercise in Hot Weather

Take steps to exercise safely when the weather is hot.

  • Check the weather report to see if it is safe for outdoor exercise.
  • Stay hydrated.
  • Wear light coloured, loose, comfortable clothing.
  • Check your blood sugar.

High heat and humidity causes higher heart rates and blood pressures during exercise. Heat and humidity may also cause shortness of breath even with normal activity. You may also feel irregular heartbeats (palpitations), light-headed or dizzy. 

Hot days also increase the smog and pollution in the air. Smog and pollution may also cause irregular heartbeats, light-headedness or dizziness. See the Heat Safety Index and Air Quality Health Index to see if it is safe for outdoor exercise. 

Follow these steps.

  1. Check the weather report.
  2. Stay hydrated.
  3. Wear light coloured, loose, comfortable clothing.
  4. Check your blood sugar.

1. Check the Weather Report

Check the local weather report at the time of your exercise, and note the temperature, humidity and the air quality (smog alerts and the air quality health index).

Check the Heat Safety Index

The Heat Safety Index can help you decide if it is safe to exercise and go outdoors. This index uses temperature and percentage of humidity (how much water is in the air) to create four safety zones: safe, alert, danger and emergency.

To use the Heat Safety Index: 

  1. Find the current local temperature along the bottom of the scale.
  2. Find the current percentage of humidity along the left hand border of the scale.
  3. Find the point on the graph where these two points come together. See what safety zone this point is found in.
  4. Follow the instructions in the 'what you do for each heat safety zone' chart.

Heat Safety Index


Safety zoneWhat to do
Safe Zone
  • Exercise as usual.
  • Safe to exercise outdoors.
Alert Zone
  • Decrease your exercise intensity (slow your walking pace).
  • Watch for signs (such as shortness of breath, increased tiredness).
Danger Zone
  • No outdoor exercise.
  • Exercise in an air conditioned environment only.
Emergency Zone
  • Avoid going outdoors.

Check the air quality

It is important that you check the air quality before you exercise outdoors. When you check the air quality you are seeing how much air pollution there is. Air pollution happens when many pollutants (a substance that is harmful to your health) are in the air. Air pollution is a health concern for all people. It is an even greater concern for people living with heart or lung disease, older people and younger children.

When you check the weather report for air quality, look for the Air Quality Health Index (AQHI). Air pollution can be measured by the AQHI. This index tells you the level of common air pollutants. 

In Ontario, the range for the index is 0 to 10. The lower the number, the better the air quality. If you live outside of Ontario, go to your local public health website to find out how your area lists the air quality index.

To use the Air Quality Health Index:

  1. Check the air quality index before you exercise outdoors.
  2. Follow the instructions in the 'what you do for each air quality category' chart.

Air Quality Health Index (AQHI)

AQHI numberRisk levelWhat to do
1Low Risk
  • Exercise as usual.
  • Safe to exercise outdoors.
4Moderate Risk
  • Decrease your exercise intensity.
  • Watch for signs.
  • Consider rescheduling your outdoor exercise.
7High Risk
  • No outdoor exercise.
  • Exercise in an air conditioned environment only.
Above 10Very High Risk
  • Avoid going outdoors.
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2. Stay Hydrated (ensure you drink plenty of water)

Drink water before, during and after your exercise. Dehydration (loss of body fluids) can lead to higher heart rates, shortness of breath and feeling dizzy. 

If you exercise for up to 1 hour, follow the guidelines below.

  • Drink 6-8 ounces of water (about 175 to 240mL) before you exercise.
  • Drink 6-8 ounces of water (about 175 to 240mL) every 20 minutes during exercise and after you cool down.
  • Do not wait to drink water until you feel thirsty.
  • Speak to your doctor if you have limits on how much fluid you can have each day.
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3. Wear Light Coloured, Loose, Comfortable Clothing

This clothing reflects the sun and allows air flow to help you stay cool.

  • Choose a fabric that helps sweat move away from your body. Dry wick (synthetic man-made) fabrics work best. 
  • Wear a hat or visor and use sunscreen to protect your skin. 
  • If you are traveling, give yourself about a week to adjust to the new temperature.
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4. Check Your Blood Sugar

Your blood sugar changes based on the weather. Each person responds differently. 

Your blood sugar levels can lower in hot weather. 

  • Your blood sugar is lower because your blood vessels in your skin open wider. Your blood vessels are open wider to keep you cooler. 
  • Insulin acts quicker during warm weather. 

Your blood sugar can also be higher in hot weather.

  • Higher blood sugar happens when you are dehydrated (loss of body fluids).
  • Higher blood sugar happens when your body is under stress, such as dealing with the heat and humidity. 

Be aware and check your blood sugar more often in hot weather. 

Some diabetes medicines make you more likely to become dehydrated and sunburnt. Talk to your doctor or pharmacist about your medicines.

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Last Reviewed: 10/16/2016