First introduced to the United States in 1989, stability balls -- also known by a variety of other names including Swiss balls, fitness balls, Pilates balls and yoga balls, introduce constant instability to your workout, forcing your core muscles to engage actively during every exercise. Each stability ball inflates to a specific diameter, measured in centimeters. The most common exercise ball sizes are 55cm and 65cm, although you might find exercise balls as small as 30 or 35cm and as large as 85cm. But you'll only get an effective and safe workout if your stability ball is properly inflated.
Why Proper Inflation Matters
When a stability ball is properly inflated, it provides the right amount of give and support for a comfortable workout. It also, assuming you've selected the right sized ball to fit your body, aligns you properly for exercises. An over-inflated ball will be so rigid that it's very hard to balance on, and more likely to burst since it's under greater pressure. An under-inflated ball will be too easy to balance on, defeating the purpose of using the stability ball in the first place.
Inflating the Ball
Many stability balls come packaged with a small hand- or foot-operated air pump. The few models that don't include a pump usually come with a small needle or cone-shaped adapter that inserts into the ball's air valve. You then attach any small bike pump to the adapter and inflate the ball. Once the ball is inflated, you place the plug -- which also came with the ball -- in the air valve to seal it.
Measuring Inflation
There are three ways to measure whether your stability ball is inflated to the proper diameter. Some balls come with a strap that attaches to the air pump before you insert it into the ball's air valve. The strap wraps around the deflated ball and, once the strap goes tight around the ball, you know it's reached the proper size.
Your other option is to note the ball's target diameter, which is listed on the packaging material and might also be printed on the ball itself. Either place a piece of tape on the wall at the same height as the target diameter, or place a heavy box or piece of furniture that same distance away from the wall. Place the deflated ball beneath the tape mark or between the box and wall. Once the ball just reaches the tape or touches the box, it's at the proper diameter.
Checking Inflation
Stability balls naturally lose air over time. To check whether your ball is still properly inflated, sit down on it. A properly inflated stability ball should compress about six inches beneath your weight. Another way of checking the ball's inflation is to note your joint angles when you sit on it. Check the angles when you first inflate the ball: If it's the proper size for you, both your hips and knees should be bent at a 90-degree angle. If, over time, you notice that the joint angle at your hips or knees has changed, it's time to reinflate your ball.
Other Uses
Stability balls have many uses. Some balls are specially designed to withstand the impact of repeated bouncing and can be used for cardio training. You can use a stability ball as a weight bench for conventional weight training exercises, as a stretching aid, or as a desk chair. No matter what you're using the ball for, you'll be more comfortable if it's properly inflated.
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