How cold is too cold to exercise outside? Rachel Schoutsen Health and Weather. As life in lockdown continues, Canadians have had to get creative with their workout regime -- and for many, it meant heading outside. However, as the coldest months of the year are now underway, it's important to know the potential risks involved in taking your workout outdoors during winter. “Through my research, the threshold of -15 C is something individuals and habitually active Canadians should pay attention to,” says Michael Kennedy, Associate Professor at the University of Alberta who specializes in Kinesiology and Recreation. The reason for this is respiratory distress. Kennedy and his team conducted a study that tested athletes running on a treadmill in the following temperatures: 0, -5, -10, -15 and -20 C (40 per cent humidity).