Breathing Tests

One of the most important muscles in your body is the diaphragm. This large flat muscle allows us to breathe air in for oxygen and to breathe out to get rid of carbon dioxide. There are two general tests we can use to measure the effectiveness of the diaphragm muscle.

Breath-Holding Time is a simple test that measures the general capacity of the diaphragm. It’s easy to perform: Take a deep breath and see how long you can hold it. Anyone in good health should be able to hold the breath for at least fifty seconds. If you can’t, it may indicate some functional problem.

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Vital Capacity is a general measure of lung capacity, and a good test for measuring general diaphragm function. Vital capacity can be measured with a handheld spirometer, or with more accurate units that also measure the rate of expired air. The spirometer measures, in cubic centimeters (cc), the amount of air that you can force out of the lungs. This figure can be converted to a percentage of normal capacity, as related to your height. This conversion can be made by your doctor or calculated by the charts that accompany spirometers. You should be at least 85 percent to 110 percent on scale (which goes up to 120 percent). Vital capacity is also related to physiological age: the lower the vital capacity, the older you may be physiologically, and vice versa.

Lowered Breath Holding Time and Vital Capacity usually indicate less than adequate diaphragm muscle function. Most often, it’s due to improper breathing (see chapter 25). This is not necessarily related to VO2max, as even athletes with substantial oxygen uptake can have reduced diaphragm function.