THE CLASSIC SITUP is a workout staple. Whether you learned how to do the movement in gym class or from watching a Rocky training montage, you've probably performed more than a few sets over the years ...

The runner's plank is an alternative I use as a certified trainer when sit-ups aren't possible, and this is exactly how to do ...

Both sit-ups and crunches can help target your core muscles, but there are key differences between the two ab workouts.