An Australian summer gives runners two very different kinds of heat. A steamy morning in Brisbane or Darwin feels nothing like a dry, still afternoon in Perth, Adelaide or out west, even at the same temperature. Knowing which one you’re dealing with changes how you pace, what you wear and how you plan fluids and electrolytes.
Why heat makes running harder
Running makes heat. Your body gets rid of most of it by sweating: sweat sits on your skin, evaporates and takes heat with it. Anything that slows that evaporation makes it harder to stay cool, and that’s where humidity comes in.
Dry heat
In dry heat the air holds little moisture, so sweat evaporates almost as fast as you produce it. Cooling works well, and dry heat often feels milder than the thermometer says.
The catch is that you can lose a lot of fluid without noticing. Your skin may stay fairly dry, your mouth and throat dry out quickly, and thirst can feel stronger than on a humid day. Wind and sun add to it. Don’t judge how much you’re sweating by how wet your shirt is.
Humid heat
In humid heat the air is already loaded with moisture, so sweat struggles to evaporate. It drips off rather than cooling you, and your body responds by sweating more. That’s why a humid run can feel tougher than a hotter run in dry air.
The Bureau of Meteorology’s "feels like" temperature in its forecasts takes humidity and wind into account, and it’s a better guide for planning a run than the air temperature alone. Expect a soaked shirt, a higher heart rate at your usual pace and slower recovery afterwards.
Adjusting your training
- Ease in. Your body adapts to heat over the first couple of weeks of regular exposure. Keep early-summer sessions shorter and easier.
- Run by effort, not pace. Your normal pace will cost more in the heat. Use effort or heart rate and accept slower splits.
- Pick your time. Early morning is usually the coolest, but in humid places the air can be at its most humid then. Check both temperature and humidity.
- Find shade and loops. Shaded trails and short loops past a tap or your car make it easy to refill and cut a run short if needed.
- Dress for it. Light, loose, light-coloured clothing, a cap or visor and sunscreen.
- Tell someone. For long runs in the heat, especially on trails, let someone know your route and when you’ll be back.
Fluids and electrolytes
You lose sodium in sweat along with water, and more sweat means more of both. General practice for long runs in the heat is to drink to thirst, carry or plan access to water, avoid drinking much more plain water than you need, and include some sodium.
FastChews are a simple way to carry electrolytes without mixing anything. Two tablets contain 100mg sodium, 30mg potassium, 10mg calcium and 6mg magnesium, and the label directions are to chew 2 tablets for every 30 minutes of exercise and drink water as needed. On longer runs where you also need fuel, Energy Gummies add 36g carbohydrate, 130mg sodium and 40mg potassium per packet. On hot days, start your schedule early rather than waiting until you feel flat.
Our electrolytes for running guide sets out a plan by run length.
Know when to stop
Feeling hot and tired is normal in summer. Feeling dizzy, confused, nauseous, unsteady, or suddenly cold or shivery in the heat is not. Stop, get into shade, cool down with water on your skin, sip fluids and get help if you don’t improve quickly. A missed session costs far less than pushing through.
The short version
Dry heat cools you well but dries you out quietly. Humid heat makes you sweat more and cool less. In both, slow down, run at the cool end of the day, plan water and electrolytes for anything long, and stop if something feels wrong.
This article is general information, not medical advice. Talk to your doctor before starting a new exercise program or if you have a health condition.