Useful in developing body balance, it teaches you how to balance and this thing will let you control some of the body and teaches you to sit in the proper way. - Abdominal muscles in the abdomen..- Those suffering from compatibility problems in the spine, hip, and pelvis, because it relieves pressure on these areas..The exercise ball is taken according to the user's height. 55 cm (Small) from 150 cm to 160 cm height 65 cm (Medium) from 160 cm to 170 cm 75 cm (Large) from 170 cm to 180 cm 85 cm (XL) from 180 to 190 cm 95 cm (XXL) from 190 to 200 cm for basketball players. ...Price varies by size: 55 cm size for 60 65 cm size for 70 75 cm size for 80 85 cm size for 90 95 cm size for 100 SAR.