hussane wrote:

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what is he trying to do

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Well... it's an Ab Ball you're supposed to use it for Abdominal or Balance exercise.... we use them in the gyms here:(see definition below).... and as soon as he jerks up.... the ball is going to probably shoot out from underneath his feet and the weight of the lift is going to trust him backwards land him on his flat on his back.

 

A woman performing weighted situps on 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 sit 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. However, there is no scientific evidence of those benefits occurring by just sitting without additional exercises. ^] Using a Swiss ball as a chair is sometimes prescribed by physical therapists for back patients in sedentary jobs. However, some people warn against using a Swiss ball as chair due to ergonomical considerations.