Physio ball, exercise ball, stability ball, fitness ball — whatever you call it, we think a ball is must have for just about everyone. A stability ball can be used in the office and the gym — with a ball, basic exercises like sit-ups or push-ups become much more challenging and effective. If you're new to this piece of fitness equipment, here are some details you should know.

Sizing and Sitting

You need to buy the correct size ball for your height. The diameter of the ball makes all the difference — size does matter. If you are close to the cut off point between sizes, try testing out both sizes and see which works best for you. Here are basic guidelines to follow:

4'11" to 5'4" height: 55 cm ball
5'4" to 5'11" height: 65 cm ball
5'11" to 6' 7" height: 75 cm ball

An exercise ball, when size properly, makes for an active chair when sitting at a desk. You should be able to sit with your knees at a right angle and your thighs parallel to the ground. Aside from keeping your core engaged, replacing your seat with a ball will help your posture. Celeb trainer David Kirsch endorses the switch! If you still need convincing, here are more reasons to swap your chair for a ball.

Strength Training

You can also use the ball, to replace a weight bench for exercises like pec flies or some triceps-toning skull crushers. Simply, lie with the ball supporting your upper back and head, and work your arms while stabilizing your unsupported core with your abs, glutes, and legs. Using the ball as a bench replacement, transforms these upper-body moves into full-body exercises. Here's step-by-step instructions to work the back of your amrms lying on the ball.

The exercises you can do with one of these stability balls is practically endless. We have created a full-body ball workout. So grab your stability ball try moves like hamstring curls to tone your backside and planks on the ball, which will tone just about everything. You can also use the ball as a tool to focus on a certain muscle groups, like the abs. Watch this video of five ab exercises you can do using a ball, including tips on how to take sit-ups on the ball to the next level.

Yoga and Stretching

An exercise ball can work as a yoga prop to deepen stretches or support your body in difficult poses. A ball is the perfect prop to help you master tricky yoga poses like the advanced arm balance Scorpion. If you are working on this variation of forearm stand learn how to use the ball with this video. If stretching is more your scene, lengthen the front of your body by reclining with your back on the ball. This stretch is great after a long bike ride or a long day hunched over your computer.