You want to get out on your bike (you're training, you're meeting some friends, you're avoiding a home project, etc.) but the weather is a delightful shade of Hades. Should you go?
Let's review how to avoid heat-related illnesses, because dropping like a stone isn't a great way to end a ride.
Heat exhaustion is the first sign of trouble, and happens when your body starts to have difficulty maintaining a healthy core temperature.
As your core temperature rises, your performance drops. This not only means that your training is going backwards but it's also when you start making mistakes, and the risk of having an accident increases.
If you experience any of these, stop exercising, seek shade, and drink.
(No, not beer. Unless you're reading the comments.)
Then you're on a slippery slope to heat stroke, which is life-threatening, particularly as you may not be aware of what's happening to you.
...seek immediate medical attention.
Rather than heading out solo on a hot day, a riding buddy is a great idea. You can keep an eye on each other's condition while swapping stories about the muppet who almost took you down at Three Peaks.
You're not immune to heat-related problems, either -- radial heat occurs off-road, too. (Ever wondered why the bowl at Eagle MTB Park feels like the seventh circle of hell in summer? Now you know why.)
Always check the CFS website before heading out.
On total fire-ban days, mountain-biking is banned in all forestry reserves. This is a great excuse to stay inside and keep cool. If you can't go for more than an hour without touching your bike, maybe give it a clean instead.
When it's hot, stay safe with these simple rules: keep out of the heat, keep your fluids up, take breaks when you need them, and don't try for a PB when you could fry an egg on the asphalt.
(And also try not to read the comments.)