If Sunday's running of the 87th Tely 10 in St. John's proved anything, it's the power of heat — particularly the amount of damage that can be caused when temperatures and humidity are both soaring.

The Tely 10, an annual 10-mile road race organized by the Newfoundland and Labrador Athletics Association, was marked this year by high heat and humidity.

During the race, first responders treated numerous runners along the 10-mile route, with a few dozen sent to hospital for more intensive treatment. One runner, Mark Didham, was put in a medically induced coma to deal with heat stroke that threatens his organs.

To find out more about heat exhaustion and heat stroke, CBC News spoke to Dr. Brian Metcalfe, an emergency room doctor who also volunteered as a first responder during the Tely 10 through St. John Ambulance. 

Here are some things to know: 

It's serious. Heat exhaustion can lead to heat stroke, which has grave consequences. "It can be life-threatening if it progresses to a certain point and oftentimes requires hospital treatment and management," Metcalfe said. 

It can play with your mind. Confusion is a common symptom for people who have heat exhaustion. "Your body cannot really thermal-regulate itself any more and you have altered mental status," said Metcalfe. Your sense of direction can be affected, such as when some runners have trouble staying on a straight course. In some cases, you can be left unconscious. 

When 'no sweat' means a big problem. Pay attention to perspiration coming from your body, or a lack thereof. "[Some] people are finding themselves either sweating profusely [or] if you've completely stop sweating — that's obviously an indication that you need to get out of the heat," Metcalfe said. 

Stay hydrated. A water supply is as essential on a hot day as sunscreen. One of the key ways to fight heat and humidity is to drink plenty of water, and regularly — but not too much; excessive intake of water can actually be toxic to the body. Steady hydration applies not only to people who will be exerting themselves through sports, but also those just resting at home. 

Find a breeze. You can regulate your temperature, and overall comfort, by looking for a breezy place. Fans can help cool down your skin. 

Lighten up. There's a good reason why tennis players like white uniforms. Dark clothes can make you even more uncomfortable on a hot, humid day. "Wearing light-coloured clothing and lightweight clothing is also helpful for shedding the heat." 

Check on others. While looking after yourself and your immediate family, keep in touch with seniors and others who may be vulnerable in high temperatures. "It's an issue we see ever year across the country — many unfortunate cases with elderly people in homes alone. Maybe they don't have air conditioning, maybe they don't have access to water, maybe they have other health issues and they find themselves in trouble." 

With files from Debbie Cooper