Exercising Safely in Heat

June 16, 2016


Have you noticed your workouts feeling even tougher than usual lately?  Rising temperatures and humidity could be one reason you feel like you’re working harder than ever before.  Here’s a basic guide to what’s going on inside your body during an exercise session in heat, and some things you can do to make sure that your discomfort doesn’t turn into a heat-related illness.


What’s going on?


During exercise, your body creates heat as a product of the cellular respiration (energy production) taking place within your muscle cells.  In order to release that heat, your body circulates additional blood to the surface of the skin in order to release the excess heat into the environment. This leaves less blood available to bring oxygen to your working muscles, and as a result, the work that you do feels harder than it would under cooler conditions, and in fact, it is.  For every degree that your body’s core temperature raises, your heart rate will increase by about 10 beats per minute.

Your body will also attempt to release heat through sweating.  The sweat evaporates off of your skin and cools your body temperature as it dries.  In humid conditions, this mechanism is less effective at helping your body lose heat, although your body will continue to sweat.  


How much do I need to drink?  Is water enough or should I bring Gatorade?


You should drink 8–12 oz. of water 20–30 minutes prior to exercise plus 6–10 oz. additional water for every 30 minutes of exercise to help prevent dehydration. For HIITLAG classes, water is enough, and sports drinks add unnecessary sugar and sodium to your diet.  However, if you’re participating in intense exercise that lasts longer than 1 hour, you may need to replenish lost carbohydrate and sodium with a sports drink.


What else can I do to avoid overheating or overexerting myself?


One great way to gauge exercise intensity is using the RPE or Rating of Perceived Exertion scale.  This is a 0-10 scale, where 0 represents no activity and 10 represents an all out maximum effort.  


0-3 light exercise, you are able to easily hold a conversation  

4-6 moderate intensity exercise, you should be able to speak in short sentences, but talking is becoming more difficult  

7-9 vigorous effort that you can only sustain for a short time, you can speak in one or two word bursts

10 maximum effort, you cannot speak


If you’re a HIITLAG veteran, you belong in the 7-9 or sometimes even 10 range during our work intervals.  If you’re newer to HIITLAG or new to fitness in general, levels 4-6, with an occasional 7 is appropriate as your body (and mind) adjusts to interval training.  If you maintain an appropriate RPE, no matter what the conditions, your own body will be able to guide you and keep your intensity at a safe and appropriate level.  In practice, this may mean taking more frequent breaks during class, or sitting out an interval or two, to allow your body the extra recovery time it needs to stay in your RPE range.


Will my body learn to adapt to heat?


Yes!  After 8-14 days of exercising in hot and humid conditions, your body will begin to make some physiological adaptations to exercising in heat.  You will begin to sweat sooner and sweat more and your blood volume will increase in order to be able to shunt more blood to the surface of the skin for cooling.



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