An ab ball is better known by the names stability ball, Swiss ball or exercise ball. The ball trains the core muscles, which stabilize the torso, so just lying or sitting on the ball begins to work the abs. Crunches on an ab ball bring more results. Using the right-size ball is important.
Sizes
Ab balls are inflatable and are made in different sizes. Centimeters are the unit of measurement that ab balls are sold in. The standard sizes are 45 cm, 55 cm, 65 cm and 75 cm. Smaller and larger sizes exist, but are less common and are unlikely to be found in a gym or in a sporting goods store. Although most people can use either a 55-cm or 65-cm ball, not everyone will find these sizes comfortable or workable for ab exercises.
Average People
The American College of Sports Medicine (ACSM) recommends a 55-cm ball for people between 5'6" and 6' tall. If you are between 6' and 6'5", try a 65-cm ball. There is overlap because your leg length affects which size ball is best for you. A long-legged 6-footer will likely prefer a 65-cm ball, whereas someone of the same height with a long torso and short legs may prefer a 55-cm ball.
Larger Sizes for Taller People
If you are taller than 6'5", try a 75-cm ab ball. Even people who are only 6 feet tall might use this size, depending on leg length. Larger balls that are 85 cm accommodate very tall individuals. If you are over 6'9", first try an 85-cm ball.
Smaller Sizes for Shorter People
A 55-cm ab ball may be too large for some people. If the ball is too large for you, your feet won't be able to touch the floor completely when doing ab exercises like ball crunches, so the risk of falling increases. The ACSM suggests that people 5'5" and shorter use a 45-cm ball, though if you are under 4'10", then a 30- or 35-cm ball may be more comfortable.
Checking Your Ab Ball
Although the sizing guidelines are helpful, there is a simple test that lets you know if you have the right-size ball. Inflate the ball until it is the size advertised. Place a measuring tape around the ball to check the diameter; it is possible to over-inflate an ab ball. Sit up straight on the ball with your feet flat. If your thighs are parallel to the floor with your knees bent at right angles, you have the correct size, according to the ACSM.
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