This simple floor exercise is redefining how Americans train their core—without crunches, machines, or strain on the spine.

When we think of core exercises, standard moves like situps and crunches are often a go-to. But working the side body is an important piece of a well-rounded core routine that is sometimes overlooked.

For on-demand core workouts — plus fitness challenges, meal plans and inspiration — download the Start TODAY app! When we think of core exercises, standard moves like situps and crunches are often a ...