vital capacity The total amount of air that can be exhaled after maximum inspiration. The vital capacity of an average human is about 4.5 litres; in trained male athletes it can be 6 litres or more. However, some air always remains in the lungs (see residual volume).

vital capacity (vy-t'l) n. the maximum volume of air that a person can exhale after maximum inspiration. forced v. c. (FVC) the maximum volume of air that the lungs can expel in a forced expiration after the deepest possible inspiration.