Exercise balls -- also known as physioballs, Swiss balls, gymballs or fit balls -- are large, vinyl balls you can use to strengthen and stretch your body, improving core stability and balance. What size Gymball do I need?
If you're between 155cm and 170cm, a 55cm ball is a good choice. If you're between 173 centimeters and 185cm, try a 65cm ball. If you're 188cm or taller, try a 75cm ball. Air pressure counts, too