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, ...

Cardio (also called cardiovascular exercise or aerobic exercise) is an important part of staying physically fit. During cardio, your heart beats faster, pumping oxygenated blood throughout the body.