What’s the deal with those big bouncy balls taking up space around the gym? Stability balls (also called exercise balls, balance balls, Swiss balls, or fitness balls) are more than just fun to sit and bounce on—they’re a great way to improve strength, cardio endurance, and balance. By tackling basic moves (like push-ups, squats, and planks) on an unstable surface, muscles get more bang for their buck . Stability balls are also great for getting back into shape after an injury because they can reduce muscle and spinal strain during certain movements .

To get the most from a bouncy fitness routine, make sure to choose the correct size stability ball. (Note: some moves below use a larger or smaller than normal ball. For most exercises, though, it's best to have correctly sized equipment.) Most balls come in three diameters based on the user’s height: 55 cm for those between 4’11” and 5’4,” 65 cm for people between 5’4” and 5’7,” and 75 cm for tall drinks of water between 5’11” and 6’7.” A good rule of thumb for finding the right fit: Sit on the ball and make sure the hips and knees are at right angles with the floor.

Reps and sets will depend on fitness levels, but for most of these exercises we recommend doing 3 to 5 sets of 10 to 20 reps. After a few workouts, try bumping up the reps to really test that strength. Ready to go? These moves take the stability ball way beyond the basic crunch.