Fitness balls go by many names including exercise balls, stability balls, physio balls and balance balls. Fitness balls were originally used in Europe in physical therapy and rehabilitation clinics. In the 1980s, American physical therapists visiting Europe brought back the information and knowledge about exercise balls. By the 1990s, these balls became an integral part of athletic and fitness training.
Identification
Fitness balls are large, inflatable balls that can be used for various exercises and balance activities. These balls are made of rubber. The more expensive balls are made of anti-burst PVC plastic. If the ball breaks while you are sitting on it, it will slowly deflate as opposed to bursting explosively.
Sizes
Fitness balls are measured in centimeters and are available in three standard sizes --- 55 centimeters (cm), 65cm and 75cm. Depending on the brand, you may also find 30 and 45 centimeter fitness balls available.
Height Chart
One method for sizing your fitness ball is by your height. Most exercise organizations and equipment manufacturers provide height and size charts for fitness balls. You simply choose the ball size based on your height. The American Council on Exercise (ACE), a non-profit fitness organization, suggests a 30cm ball if you are under 4 feet 6 inches, a 45cm ball if you are between 4 feet 6 inches and 5 feet, and a 55cm ball if you are between 5 feet 1 inch and 5 feet 7 inches. If you are between 5 feet 8 inches and 6 feet 2 inches, ACE recommends a 65cm ball and if you are over 6 feet 2 inches, you should use a 75cm ball.
Sit Test
If you have access to a fitness ball or are at a gym and trying to choose a ball, sit on the ball to test the fit. When sitting on the the ball, your knees and hips should both form a 90-degree angle. Your upper thighs should be in line with your hips and parallel to the ground. If your knees rise above your hips, the ball is too small, if they fall below your hips, the ball is too large.
Considerations
Not all organizations provide the same height and ball size recommendations. For example, the size chart by Gaiam, a popular fitness ball maker, only refers to three ball sizes --- 55, 65 and 75 centimeters. Gaiam's height recommendations are slightly different than the ACE chart. The American Council on Exercise notes that the firmer the ball, the more difficult the exercise, and the softer the ball, the easier the exercise. ACE recommends that those who may be out of shape, overweight or beginners start with a larger, softer ball.
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