OM is right, at least for me. If I am hiking, as long as I keep my hands and head warm, I can work up a sweat in no time. And that's not good in the winter. So the challenge is taking enough layers to keep myself warm after I stop the exercise.

My wife, who runs cooler in any weather, likes to make sure she never feels even a little cold. Me? If I am not cold when we start, I will be dripping with sweat within fifteen minutes of hitting the trail.