I seem to have difficulty getting my Sissel Swiss Ball Pro (65cm / 26" / Purple – purchased from Ridgeline Fitness) to reach its maximum size.
(Photographed with a Fuji F200EXR, and edited in Adobe Photoshop Lightroom 2)
65cm / 26" is the specified diameter / height of the ball. My Swiss Ball is already at about 24 inches high, and it feels like I can't pump in any more air into it.
A Google search gave me the following references on the proper way to inflate a Swiss Ball.
Pop Goes The Swiss Ball! – Jim Waitakere wrote:
Apparently the ball is meant to be soft after inflation. When you sit on it your legs should form a 90° angle. The ball will stretch with age and will require more air over time. The 65cm probably will only be reached after several months of use although as far as I am concerned an ‘Anti-Burst’ 65cm ball should be able to be inflated to that size right away – if not then why don’t they call it a 50cm ball and be done with it?
Correct Swiss Ball Inflation – In this post, Jim shares some photos of the Swiss Ball, plug and how the ball should look like "… when you sit on it your lower and upper leg forms a 90 degree angle i.e. your thigh should be parallel or slightly above parallel to the ground."
Exercise Ball Care – Inflating the exercise ball:
Unless you achieve sitting comfort sooner, continue adding air until the exercise ball reaches the level of the mark, then stop. Do not over-inflate the ball! You should be able to push the ball inward roughly 2" when it is fully inflated.
Stability Ball Basics – numberoneme.com shows what a properly-inflated ball should look like.
(Click to watch in HQ on YouTube)