The goal is to support your posture and relieve back strain. Once the ball is inflated, sit on it and check for the following:
Hips vs. Knees: Your hips should be about 5–10 cm (2–4 inches) higher than your knees. If your knees are higher than your hips, the ball is too small or under-inflated.
Feet Placement: Both feet should be flat on the floor, spaced about shoulder-width apart for stability.
Stability: You should feel stable and supported, not like you are wobbling or about to tip over.