Exercising in the heat of summer brings special challenges. Hot weather can affect your body. Being hot is not just a matter of being a bit uncomfortable and sweaty. It can seriously affect your health and your ability to exercise. Still, if you know the warning signs of heat stress and take basic steps to manage the risks, summer is a great time to be outdoors and active.
Your body works best within a very narrow range of temperature. Your resting temperature is about 37 C. Many parts of your body work together to make sure that you do not move too far from this temperature, even when exercising hard in hot weather. Throughout the day, your body temperature depends on how much heat you make in your body and how much you can remove. Even marathoners or triathletes working hard are usually able to keep their body temperature from going above 39 to 40 C. However, in some cases the body’s control systems can break down or not be able to keep up.
As it heats up, your body’s first defense is to increase blood flow to the skin. Blood vessels in your skin dilate (widen), allowing heat to move from your warm body through your skin to the cooler air around you. If you are moving quickly, as with cycling, this helps release heat into the air to keep you cool. However, if it is a very warm day, there is little difference between your skin temperature and that of the air around you. In this situation, losing heat through your skin does not work as well.
The other main way to lose heat is through sweating. As you get warmer, sweat on your skin is heated by your body and evaporates into the air. Sweating is a very good way to release heat from your body, especially when the air temperature is high. However, there are some important things to keep in mind.
Over the past two decades, health messages suggested that you should always drink as much water as possible, and that any little bit of fluid loss from your body would harm your athletic performance and even your health. As a result, it is now common to see water bottles strapped to children and adults alike. However, the amount of water that you actually need to drink is a matter of strong debate. Some of the latest findings and suggestions may contradict what you have been taught.
Summer is an ideal time to exercise outdoors. With a little knowledge, you can enjoy yourself and stay safe in the heat.
The heat that your body makes during exercise is the largest source of heat gain in the body. When you are running or even just sitting still, 80 per cent or more of the energy being released from food is in the form of heat. Only 20 per cent or less is actually used to move your muscles or keep you alive. If your body cannot get rid of this heat and it builds up, you will get too hot very quickly. At this point, many systems in your body are affected. Your heart must work harder to pump enough blood to your muscles to keep you moving. Your skin and sweat glands must also get rid of the extra heat.
The chemistry and activity in your brain can also be affected. These changes in your brain make you feel more tired when it is very hot outside. Your brain is very good at keeping you safe in the heat. That tired feeling you have when it is hot usually makes you not want to exercise as hard, so you will generate less heat in your body. Listen to your body and how it is feeling, and only exercise as hard as is comfortable. Do not push yourself.
Note that some prescription medications, especially many anti-depressants, can change how hot you feel. You may feel less hot than you actually are. Check with your doctor about your medication before exercising.
When your body gets too hot from living in hot weather or from exercising, you run the risk of developing heat illness. Do not take these risks lightly. Be aware of signs and symptoms.
The humidex is a Canadian innovation. It describes how hot and humid weather feels to the average person. The humidex combines the temperature and humidity into one number to reflect how hot it feels. As it considers the two most important factors that affect summer comfort, it can be a better measure of how stifling the air feels than either temperature or humidity alone.
The humidex is divided into ranges, which indicate the degree of comfort or discomfort:
Extremely high readings are rare except in the southern regions of Ontario, Manitoba and Quebec. An extremely high humidex reading is over 40. In such conditions, all unnecessary activity should be reduced. With a reading in the mid to high 30s, certain types of outdoor exercise should be toned down or changed. The need for this depends on your age, health, physical conditioning, what you are wearing, and other weather conditions.
Avoid exercising intensely if it is very hot or humid outside, and take frequent rest breaks. If you do get overheated, find a place to cool off. In hot, humid conditions, there is considerable risk of heat stroke and sunstroke.
If exercising with your pet, remember that animals feel the heat too. When the humidex is high, ensure your pet has plenty of water to drink and protect it from the heat.
You can find out more about the humidex on the Environment Canada website.