Ottawa Race Weekend organizers are floating the possibility of cancelling running events this weekend because of hot temperatures and high humidity.

The weekend's director said Friday temperatures expected to reach the low 30s are hotter than they would like and said cancelling races is a possibility.

"We are still hoping for a change in the weather and that temperatures will stay moderate enough for a safe event," said John Halvorsen in a news release just before a noon news conference.

"However, we also need to be prepared for the worst, which is the possibility of a cancellation if temperatures pose a serious safety risk. The safety of our runners is paramount. That will be a decision that I make along with our Medical Director."

Halvorson said they're especially concerned about safety during their longer runs.

It would be disappointing,says <a href="https://twitter.com/hashtag/ottawaraceweekend?src=hash">#ottawaraceweekend</a> director John Halvorsen over possibly cancelling races due to heat <a href="https://t.co/m4ch5QFeDV">pic.twitter.com/m4ch5QFeDV</a> —@AshleyBurkeCBC

Ottawa paramedic J.P. Trottier told Ottawa Morning host Robyn Bresnahan Friday morning runners need to listen to their bodies and slow down or cool off during the race if they're not feeling well.

"The calls we get and the cardiac arrests that happen are mostly because people ignored and kept pushing because [they think] 'Oh my goodness, I'm only two, three, four kilometres away from the finish line, I'm going to keep going,' that's when they collapse," he said.

Safety over personal bests

Trottier said his first shift as a paramedic was during a similarly hot Ottawa marathon weekend 34 years ago.

Paramedic J.P. Trottier says runners should slow down if they're having trouble with the heat and linger in a cooling station if possible. (CBC)

"It was extremely hot, humid. There were some calls during the race but mostly after the race, hours after. A lot of people did not rehydrate, did not stretch properly, did not eat in a proper fashion to replenish the minerals you lose through perspiration. That's very important," he said.

Trottier said drinking water is important but people also have to pay attention to the minerals they lose when they sweat.

"Your muscles work on those minerals," he said.

"As a reminder, your heart is a muscle. When we see the cardiac arrests that's because people have lost copious amounts of sweat and they just have nothing left. The heart will just stop."

Doug Duff says keeping hydrated in the days leading up to a race on a hot day is important to stay safe. (CBC)

Runner Doug Duff, who's set to run his ninth marathon on Sunday, said Friday he's "a little concerned" about the forecast and is prepared to toss his target time aside.

"Being in tune with your body and knowing the signs [of trouble]: light-headedness and dizziness can come on with overexhaustion and the heat," he said.

"Just being really aware of those signs and if any of those come on, just pull back the reins and worry about staying safe rather than gunning for your goal."

Shorter races are scheduled to start Saturday afternoon, while the half marathon and marathon are set for Sunday morning.

Organizers are looking at the possibility of moving the start times of races, said the weekend's Facebook account in response to a comment.

We’re also asking residents to please turn on hoses and sprinklers for runners as they pass by during the weekend —@OttawaMarathon

What to do

The race's medical director Dr. Jon Hooper has posted advice on avoiding dehydration and heat illness when running in hot weather on the weekend's website: