It's 20 Degrees Warmer than it Is

Yes it is.  Beware of heat exhaustion.  In the winter.  Believe it or not, you can suffer from heat exhaustion when it is -30 degrees Fahrenheit.  A new employee at my workplace served in the Army for six years, and for a few of those winters he was stationed in Fort Drum, NY, which is within spitting distance of Canada.  You can safely bet that it gets chilly up there.  Despite that, he said that some guy's would still manage to get heat exhaustion in subzero temperatures while doing their PT.

I'm a big fan of running outside year-round for a number of reasons, and one is the fresh air element.  I don't think it's a coincidence that each time I've ran on a treadmill inside this winter I ended up hacking up a lung for a week afterwards, whereas when I've run outside the results were much different.  As long as you can bundle up and withstand the cold, you're much better off outside.  Think about it - the windows in that fitness center probably haven't been opened since August or September.  That mean's you're breathing the same sweaty, stale air all season long.

But don't bundle up too much.  The rule of thumb my office mate taught me is to dress for weather twenty degrees warmer if you'll be engaging in strenuous exercise.  If it's zero, dress for twenty.  If it's twenty, it's above freezing.  If it it's forty, it's actually mildly warm!  If you're unsure of how to dress, wear some layers that you can easily peel off if necessary.  In the middle of winter I usually go with an Under Armour long sleeve, a t-shirt, and some sweats.  I top it off with a hat and gloves.

It's 51 today,
Jeff