Nothing is worse than a long layover at the airport. It is such as waste of time and I just sit there thinking about all the things I could be doing during that time.
Airport Gyms, Exercise on the Fly is a FREE listing of all airport gyms, airport exercise clubs and airport fitness centers available in and around select popular US (and Canadian) airports today. It is great because if you're an active traveler that would rather spend an hour in the gym (versus an hour in the terminal watching television), or would rather take a yoga class (versus wandering through trinket shops and fast food places), airportgyms.com can help you find a gym in, near or around common airports. Check it out AirportGyms.com before your next travels.
Fit's Tip: Not many airports have actual gyms in them, so most of the time you'll be directed to airport hotels (connected or not to the airport) with fitness centers in them. I would be sure you have a good chunk of time before heading on over as it may be a trek getting there.