How should I choose the right stability ball?

A rule to use is that when you are sitting on the ball, your legs should be at a 90-degree angle with your thighs parallel to the floor and your hips at the same height as your knees. However, there are some exercises you may do where a smaller ball might work better.  Most stability balls have a size in centimeters stamped on it.  If you are between 5' and 5'7", try a 55cm ball.  If you are between 5'8" and 6'2" try a 65cm ball.
The size of the exercise ball affects your ability to gain the maximal benefits and effectively perform strength exercises. When positioned, your feet should be flat and your thighs should be parallel to the ground. If this is not the case, then you may need a smaller or bigger ball. Also, the firmness of the ball makes a difference to doing exercises. It is easier to balance on softer balls with less air, whereas the level of difficulty of performing the exercises increases as more air is added and the ball becomes firmer. (This answer provided for NATA by the Saint Louis University Athletic Training Education Program.)
Stability balls are often seen in fitness facilities. You will find these in all different colors and sizes. You can sit on, lie on, or use a ball for support. You will want to find the right-sized ball for you. The right ball makes a big difference when you are sitting or lying on it. If you are five-feet-five or shorter, a 55 cm ball is the right choice; if you are five-feet-six to six feet tall, use a 65 cm ball; if you are six-feet-one or taller, use a 75 cm ball.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.