This cold snap hasn't deterred a lot of people from keeping up with their outdoor exercise routine, but for those with asthma it's a particular concern.

The frigid weather can trigger an asthma attack for cold-weather athletes and people who like outdoor exercise.

Dr. Jim Lewis is a respirologist at St. Joseph's Health Centre.

"About 80 to 90 per cent of patients with asthma will have increased symptoms on excercise, particularly in the cold weather"

As for what triggers it, Lewis says "It's mostly felt to be due to hyperventilation, or deeper breathing in the cold, dry air, when it's cold outside. So it cools the airways, they become dry and the muscles go into spasm"

To complicate things further, asthma symptoms in the cold can be different.

"Typically asthmatics might weeze or have chest tightness, in cold air they migh cough, they might feel extreme fatigue, they might have weakness."

So how cold is too cold be outside?

"In patients whose asthma are well controlled and are fit athletes, the recommendation is still not to exercise when temperatures are below -10 C," Lewis adds.

Asthma is a very common condition. In southwestern Ontario, it's estimated to affect 15 to 20 per cent of the population.

Studies also show some 40 per cent of elite cold-weather athletes suffer from symptoms of asthma.

And it's important to be aware of the symptoms.

"If you're obviously aware that it's your asthma you should probably stop exercising. If patients are having difficulty with their asthma on a day-to-day basis going out in the cold air - particularly temperatures like we've been having - can be significant and they should probably avoid that."

But whether you are an Olympic athlete or a weekend warrior, provided it's not too cold, the weather doesn't have to sideline you too much as long as you're prepared.

Lewis recommends "Try to warm up before exercising instead of going right out into the cold air and starting your activity. Warming up does help mitigate some of the symptoms. And most often taking a puffer of their reliever medication as a preventative measure prior to exercising"