To the happy, you-gotta-move-with-it music, Karen Lauer pedals fiercely on her stationary bike at the front of the room, urging participants in her spin class to do the same. As the song trails off, ...

The lighting's dim, the music's pumping and the booming bass sends vibes through your body. Sounds like a night club, doesn't it? But if the room is filled with people pedalling on stationary bikes, ...