Pull in your abs. And as we say ... Now we're going to move on to hamstring curl. Lie back, heels on the ball. Raise up, nice, straight body. Keep it nice and straight. We curl it in.

Want to work your abs with a yoga ball? We turned to an expert to walk you through the best moves to do—and how to do them.

While our abs are an important part ... a hamstring curl and a bridge with straight legs. If you don't already have a ...