Fitball,a large ball for sitting or lying on while exercising: ... while often referred to as a Swiss ball, balance ball, exercise ball, stability ball or Yoga ball.
The fitball is used for a ball based training workout that works your core muscles including the abdominals, back, bum and thighs. Simply sitting on thefitballengages your core muscles and stabilisers. ... Then move on to back, shoulder and arm exercises. It can also be used for you to strengthen and stretch your body, improving core stability and balance.
The Fitball is an important stabilizing feature in ANY Sport.
Source for information on Swiss Ball Training Techniques or customized workout programs at: https://www.andyashton.net/shop
Which size is recommended for get for your size??
Just fit the exercise ball using the 90 degree rule in sitting. An under-inflated ball will not be as firm, but it will function just fine.