Athletes must pay close attention to signals from their body as they train in extremely hot conditions, but their bodies can adapt, a scientist says.

For some top flight athletes, extreme temperatures are part of their training, said Greg Wells, a sport scientist and physiologist based in Toronto.

With the Pan Am Games coming up in Mexico, these athletes have to learn to deal with the heat, Wells said.

Part of that training includes paying close attention to signals of thirst and fatigue that could be warnings of heat exhaustion.

"I actually got heat exhaustion in Africa cycling," Wells recalled. "It actually feels like your body is shutting down. Your brain is sending signals for your muscles to move and nothing happens."

But when healthy people spend an extended period of time in heat, their bodies get used to getting rid of heat more effectively, Wells said.

"We're very good at retaining electrolytes and keeping the blood healthy, keeping the organs healthy and dissipating heat," Wells explained.

"We're also really good at absorbing more water when we drink and [staying] hydrated and we learn to manage our bodies in the heat. That happens over the course of even just a few weeks."

How the body adapts to heat

Normally, the body regulates its body temperature by pumping blood from the internals organs and the brain out to the skin where it can evaporate through sweat.

Wells said the body also adapts by:

• Developing more capillaries in the skin so the blood can circulate better and get the heat out.
• Sweating more to pull heat out of the body through evaporation.
• Learning to absorb and retain electrolytes when we sweat.
• Increasing the amount of blood.

When the body is unable to adapt to hot conditions then heat exhaustion and heat stroke, a medical emergency, can develop.

Those who want to continue to train during a heat wave should be aware of the risks, stay hydrated and stop if the heat is overwhelming, Wells advised.

For Toronto Argonaut defensive end Ricky Foley, the extreme conditions bring out the best in professional athletes working out in full football gear in 30 C heat and high humidity.

"It's not ideal, but it will probably make us tougher," Foley said.

One of the most important thing that athletes and others can do during a heat wave is to stay hydrated, experts said.

With files from CBC's Kelly Crowe