Choose a LARGER ball if any of the following applies:
1. body weight / height proportion ＞ average
This is quite intuitive as the Extra Weight would compress the exercise ball down more than usual, compromising your body alignment.
2. Legs Longer than average
Longer legs make your knees higher than your hips, easily resulting in a rounded back.
3. Using the yoga ball as a Chair Alternative
4. Back Problems
Comfort is the top concern when you use the exercise ball as a chair, yet a fully inflated exercise ball (to its maximum diameter) is too firm for you to sit on for an extended period. Therefore, choosing a larger yoga ball may be wiser as you can deflate a tiny bit and still maintain a good posture, which is key to relieving your back problems.
Note: The maximum height of your yoga ball chair should be no less than 4 inches higher than your regular chair.
5. Height is near the Upper Range
6. Novice Exerciser
A larger exercise ball means more contact area with the floor and your body, thus providing more stability and support during your workouts. If you have just embarked on your workout journey or have poor balance, then a larger yoga ball is a better option to start with.
7. If in Doubt
If you can’t decide between two close sizes, choose the larger one. You can always deflate the exercise ball later.