Men should choose the older ones, and women should choose the smaller ones. First of all, we should choose the size of the yoga ball according to the individual's figure. Yoga balls are 45cm, 55cm, 65cm and 75cm in diameter. If you are a petite lady, you can choose 45 cm or 55 cm yoga balls, while 65 cm and 75 cm yoga balls are more suitable for tall men. In addition to the choice of size, it is more important to choose a sturdy and durable fitness ball produced by regular manufacturers, which should be very elastic and full of safety. Generally, the weight of yoga fitness ball is affordable, because when we exercise, we don't put all the weight on the fitness ball, it only bears part of the weight, and our body and the ball produce a kind of antagonistic force. Fitness balls let us relax and sink, at the same time, our bodies will have their own strength to go up and tighten muscles at the same time.