Winnipeg Free Press - PRINT EDITION

How to avoid heat illness

  • Print

Summertime can bring beautiful, warm weather that invites you do your physical activity outside. If you are not accustomed to a warm climate or to exercising in warm weather, you can suffer from heat illness. Of course, the safest option would be to exercise early in the day before the heat becomes intense (before 10 a.m.) or later in the day as it starts to cool down (after 4 p.m.). However, many outdoor sports or matches take place during the day, so it is important that you prepare yourself for difficulties that can occur with exercising in the heat.

Exercising in hot weather can make you feel sluggish and even exhausted. Trying to stay cool can be a challenge depending on what type of activity you are participating in. If your activity has no cool shelter, you will probably notice that you cannot exert yourself for a long period of time. It can be so uncomfortable that you can begin to feel physically and mentally unwell. Every year, there are thousands of reported cases of heat illness in North America. The true number is likely much higher because many cases are not reported.


What happens to the body when exercising in the heat?



In cool environments, your body will transfer the heat produced from exercise directly to the air. In warm weather, heat is lost from your skin by sweating and evaporation. Your body will try to keep your inner temperature from rising more than three to four degrees. If it is very warm and humid outside, it will be very difficult to keep your inner temperature from rising to dangerous levels if you are exercising.

The intensity of your exercise is also very important in the heat. If you try to perform the same workout intensity in the heat as you would in a cooler environment, your heart will work harder, with an increase in heart rate and the amount of blood pumped out per beat. Your inner temperature and skin temperature will also rise. If you are taking part in an endurance event where you are exercising non-stop for greater than 20-30 minutes, do not expect to perform at the same intensity as you would in a cooler environment. There is nothing you can do to avoid a decrease in performance when high heat and humidity are present.


What is heat illness?



Heat illness represents a category of conditions that occur when your body cannot effectively get rid of excess heat. These include heat stress, heat cramps, heat exhaustion and heatstroke. You need to consider the outdoor temperature and the humidity when you are assessing weather conditions that could lead to heat illness. As the temperature and humidity rise, it becomes more difficult to sweat as evaporation slows down. With a temperature of 35C and humidity at 90 per cent, the body loses no heat. You obviously do not want to exercise in any environment that would come close to such conditions.


What are the symptoms and signs of heat illness?

Heat stress is an early stage of heat illness where body temperature increases, heart rate and blood pressure increase, dizziness, fatigue and mental difficulties can arise. This condition usually responds to cooling and rehydrating with water.

Heat cramps can also occur at an early stage of heat illness. A lack of sodium can lead to muscle cramps (especially in the legs), weakness, marked thirst, fatigue, nausea/vomiting and elevated heart rate. If you have heat cramps, you should seek medical attention for treatment. You can initially start treatment by resting in a cool place, stretching the cramped muscles and drinking water with some salt in it (2.5 ml salt mixed in 500 ml of water, divide into 2 cups, each about 15 minutes apart). Do not take salt tablets.


Heat exhaustion is a more severe form of heat illness where the body becomes dehydrated and loses important electrolytes. Fainting may occur, a drop in blood pressure with an increase in heart rate, nausea/vomiting, profuse sweating, cool skin, lack of urine output and headache among other signs are common. You should seek a cool place and start drinking cool water. Applying cool, wet towels and removing tight clothing is also recommended. Medical assistance should be sought as soon as possible.

Heatstroke is a very serious form of heat illness and a medical emergency. The body overheats and can no longer cool down with sweating. Signs of heatstroke include hot and dry skin (lack of sweating), confusion, faintness, staggering, combativeness, bizarre behaviour, strong rapid pulse, seizures and coma. Body organs can fail and death can result. Heatstroke requires immediate emergency medical attention. While waiting for medical evacuation, the victim should be in a cool, shaded area and the body covered with wet, cool sheets. The person should be lying down. Cold packs wrapped in a cloth are also used to cool down the large blood vessels.


What other factors can make someone vulnerable to heat illness?

If you consume any beverages on the day of your activity that are caffeinated, such as coffee, tea, alcohol or soft drinks, your body will lose more fluid, leaving you dry. Certain medications such as beta blockers, diuretics, decongestants and amphetamines can make you more vulnerable to heat illness. Clothing that doesn't allow your skin to breathe and get rid of moisture can also contribute to heat illness.

Age is also a very important risk factor. Children have more surface area relative to their body mass making them more susceptible to heat loss and heat gain. The elderly are more likely to have an impaired ability to regulate fluid loss via the kidneys. Older adults also have less blood flow to the skin making sweating more difficult.

Obese individuals are a greater risk of dehydration, since more fat and less body water leads to overheating more quickly. Certain medical conditions such as heart disease can also place an individual at a greater risk for heat illness. High protein diets contribute to dehydration and should be avoided when exercising in the heat. If you spend a lot of time in a hot environment inside or outside, you can also develop signs of heat illness without physical exertion.


How much fluid do you need to drink?

Since you will sweat more in hot weather, you will lose more fluid and you need to replace it. A general guide is to drink about 2/3 cup of water every 15 minutes of exercise. However, depending on the intensity of your workout and the exact weather conditions, you may need to consume more than this amount. Water is a sufficient fluid replacement for exercise lasting an hour or less. For longer exercise periods, you can drink a six- to eight-per-cent carbohydrate drink. Sodium loss requires replacement when you exercise for three to four hours or longer.

Do not wait for your body to tell you that you are thirsty. Drink plenty of water before, during and after exercise. Wear light-coloured, breathable clothing out in the sun. Choose an exercise time earlier or later in the day, when it is cooler. Wear sunblock and use a sun hat for shade. Know the risk factors for heat illness. Stop exercising and seek medical attention if you feel unwell.


Dr. Maureen Kennedy MD, CCFP, FCFP, MSc, PhD(c) Kinesiology, Dip. Sport Med., is a sport and exercise medicine physician at Pan Am Sport Medicine in Winnipeg.

Readers can ask Dr. Kennedy questions, but due to the volume of requests, replies are not guaranteed.

Republished from the Winnipeg Free Press print edition July 5, 2011 C1

Fact Check

Fact Check

Have you found an error, or know of something we’ve missed in one of our stories?
Please use the form below and let us know.

* Required
  • Please post the headline of the story or the title of the video with the error.

  • Please post exactly what was wrong with the story.

  • Please indicate your source for the correct information.

  • Yes


  • This will only be used to contact you if we have a question about your submission, it will not be used to identify you or be published.

  • Cancel

Having problems with the form?

Contact Us Directly
  • Print

You can comment on most stories on You can also agree or disagree with other comments. All you need to do is be a Winnipeg Free Press print or e-edition subscriber to join the conversation and give your feedback.

You can comment on most stories on You can also agree or disagree with other comments. All you need to do is be a Winnipeg Free Press print or e-edition subscriber to join the conversation and give your feedback.

Have Your Say

New to commenting? Check out our Frequently Asked Questions.

Have Your Say

Comments are open to Winnipeg Free Press print or e-edition subscribers only. why?

Have Your Say

Comments are open to Winnipeg Free Press Subscribers only. why?

The Winnipeg Free Press does not necessarily endorse any of the views posted. By submitting your comment, you agree to our Terms and Conditions. These terms were revised effective April 16, 2010.


Make text: Larger | Smaller


Key of Bart: What’s Left Of A Spent Party’s Cabinet

View more like this

Photo Store Gallery

  • A goose comes in for a landing Thursday morning through heavy fog on near Hyw 59 just north of Winnipeg - Day 17 Of Joe Bryksa’s 30 day goose challenge - May 24, 2012   (JOE BRYKSA / WINNIPEG FREE PRESS)
  • A Canada Goose cools off in a water pond Monday afternoon at Brookside Cemetary- See Bryksa’s Goose a day Challenge– Day 27-June 25, 2012   (JOE BRYKSA / WINNIPEG FREE PRESS)

View More Gallery Photos

About Dr. Maureen Kennedy

Born and raised in The Pas, Dr. Kennedy graduated from the University of Winnipeg Collegiate, earned a BSc and BA from the University of Winnipeg and an MD from the University of Manitoba in 1994. After certifying in family medicine at the University of Manitoba, Dr. Kennedy was awarded a two-year fellowship in primary care sport medicine at the University of Calgary Sport Medicine Centre. She completed this fellowship along with a MSc in Kinesiology at the University of Calgary. Her research focus was exercise counselling by family physicians. Dr. Kennedy further explored the use of exercise in medicine with PhD projects examining aerobic exercise in individuals scheduled for total hip or knee replacement surgery. She holds a diploma in sport medicine from the Canadian Academy of Sport Medicine and has served on numerous provincial and national committees for organizations such as the Alberta Medical Association, Canadian Academy of Sport Medicine, College of Family Physicians of Canada and Canadian Society for Exercise Physiology.

For the past 11 years, Dr. Kennedy has practised as a consultant in primary care sport medicine.

Dr. Kennedy's practice focuses on the diagnosis and treatment of injuries, muscle, bone and joint problems, orthopedic triage, weight management, osteoarthritis and dance medicine. She has served as the head physician for Alberta Ballet for the last nine years and has worked with the national women's hockey team along with many elite and amateur athletes in various sports. She points out that sport medicine physicians provide a tremendous service to the general public and the health-care system by shortening orthopedic waiting lists and providing non-surgical treatment options. "It's great to be back home in Manitoba and Winnipeg is a fantastic city," she adds. Readers can expect coverage on a wide range of fitness and health topics, including insider's tips on how to navigate the health-care system.


Does it worry you that, after inspection, 47 per cent of Manitoba daycare centres only received temporary licences?

View Results

View Related Story

Ads by Google