Brunette Girl With An Exercise Ball

A primary benefit of exercising with an exercise ball as opposed to exercising directly on a hard flat surface is that the body responds to the instability of the ball to remain balanced, engaging many more muscles. Those muscles become stronger over time to keep balance. Most frequently, the core body muscles — the abdominal muscles and back muscles — are the focus of exercise ball fitness programs.
Some people recommend sitting on an exercise ball instead of a chair (for example, an office chair). This is based on the theory that the abdominal and back muscles are constantly engaged and active in order to maintain proper posture and balance on the ball. There is no scientific evidence of those benefits occurring by just sitting without additional exercises. However, some people warn against using a Swiss ball as a chair due to ergonomic considerations.