Increasing lung capacity really means increasing the amount of air that is regularly brought into the lungs each minute, and thus the amount of oxygen that can be extracted and delivered by the heart and vascular system to the muscles. Typically during a normal breath we use only 10 to 15% of our lungs. The diaphragm muscle makes an airtight separation between the abdominal and thoracic cavities. During inspiration it flattens, increasing the space (and negative pressure relative to the atmosphere) in the thoracic cavity while decreasing the volume of the abdominal cavity (unless the abdominal muscle relax to offset this effect). During exercise, the intercostal muscles and other thoracic wall muscles (the accessory muscles of respiration) contract to aid the expansion (and increase the negative pressure) in the thoracic cavity. During expiration the opposite occurs in the diaphragm and accessory respiratory muscles, the thoracic cavity decreases in size, and air flows out of the lungs. With exercise conditioning, you can increase the amount of air that is regularly brought into the lungs each minute, and thus the amount of oxygen that can be extracted and delivered by the heart and vascular system to the exercising muscles. BTW: Normal adult lung capacity is 3 to 5 liters (3,000 to 5,000 milliliters). Normal lung capacity can be calculated as milliliters of air per kilogram of body weight. The equation for women is 50 to 60 milligrams of air for each kilogram of body weight (55 ml x kg), and for men the equation is 70 milliliters per kilogram of body weight (70 ml x kg). Sometimes the milliliters (or ml) is given in cubic centimeters (or cc). One cc = one ml. After age 20 lung capacity decreases. The lung capacity decreases with age possibly because of a decrease in the stretchiness, or elasticity, of the lungs & level of physical fitness. On average, both men and women lose 20 to 25 milliliters of lung capacity for each year over age 20. The equation for lung capacity by sex and age is: women ((55 ml x kg) - (22.5 X years)), men ((70 ml x kg) - (22.5 X years)). Reference Links: http://www.cptips.com/respmus.htm http://www.madsci.org/posts/archives/Apr2003/1050155434.An.r.html

Lung capacity refers to volume of air that a person can force out of their lungs after taking their deepest possible breath, this is measured using a spirometer. Exercise does not make your lungs 'bigger' but it allows you to use more of your lungs, at rest you only use a small portion of your lungs to breathe but under duress you will breathe more deeply, in response to your body's increased need for oxygen. With regular exercise your breathing will be deeper due to your respiratory system being 'stronger/fitter' for lack of a better word... hope that makes sense