It's common knowledge in fitness circles, but a lot of people don't know that the classic sit-up exercise — that staple of gym classes and boot-camp style training — is actually terrible for your back ...

The plank is one of the most effective exercises for building a stable core. But stick with it for too long and it can start to lose its edge, offering less of a challenge as your strength improves.

This series of exercises focuses on important muscles in the legs and torso we use every day. No equipment (and very little space) necessary. By Jenny Marder See more of our coverage in your search ...