Jenny Spangler and her Lake Forest, Illinois, running club will brave just about any winter weather.
"One night, we went for a run in Lake Forest when the wind chill was about 20 or 30 below zero," said Spangler, a former Olympic marathoner who coaches the North Shore club. "The path was not clear [of snow] ... and by the end we had a little trouble breathing."
But how cold is too cold to run outdoors?
"I guess a lot depends on the wind chill," Spangler said, "but if you're smart about it, there's really nothing weather-wise to worry about."
Keeping your head warm is the most important tip from experts at the American College of Sports Medicine, because more than 40 percent of your body heat escapes through it.
Stephen Weinberg, a North Shore physician and attending doctor at Weil Foot and Ankle Institute in Highland Park, Illinois, said runners should wear caps - not earmuffs - that cover the entire head.
Weinberg also said that during winter workouts, runners need to leave time to warm up so that the connective tissue in their muscles can properly transition into more intense exercise. If runners fail to warm up for 15 to 20 minutes, their bodies are more prone to cramps, spasms and muscle tears.
"The trick is to start out slowly," Weinberg said. But he noted that in cold weather, "The problem is you tend to move faster."
He also recommended beginning the workout by running into the wind and finishing with the wind at your back. That way the moisture and sweat on your body won't be as exposed to the cold.
Some of the reasons people choose not to run outside are obvious: ice, snow and frigid, cutting winds. But cold-weather exercise can take a physical toll on the body.
Mike Swisher, the training program manager for the Chicago Area Runners Association, said that aches and pains are more pronounced in cold weather because it takes longer to get warmed up, and the running landscape is harder because of ice and snow.
Spangler trained in all types of weather while preparing for the 1996 Olympics in Atlanta. The Rockford, Illinois, native does not mind training in Midwest weather but admitted she would rather work out in California than Chicago.
Most local runners hibernate for the winter, but Swisher said nearly 700 people stay enrolled in the runners association through cold weather. That compares with more than 3,000 runners typically active the rest of the year.
Swisher advises those who exercise in the cold to dress as if the temperature was 15 degrees warmer than it is. He said runners can get dehydrated or feel overheated if they are overdressed.
"If you're a little cold when you first start your run, that's a good thing," Swisher said, adding that running then becomes a way of warming up and overheating becomes less of an issue.
Swisher acknowledged finding motivation to get outdoors and exercise during the winter can be hard, but running or biking with a group is a smart way to keep inspired.
"Some might say, 'Wow, look at this: Nobody's out,' " Swisher said, "but the reality is the running community at large always keeps going."
RUNNING IN THE COLD--Layer comfortably and according to preference. In extreme cold, protect the face and hands. -Warm up with light exercise for 15 to 20 minutes. Never start by stretching; that's how pulled muscles happen. -To stay motivated, find groups to run with. -Whether running in the early winter mornings or evenings, carry a flashlight and reflective gear or tape to stay visible to traffic. -Check the weather outlook before your run.