Race is a major factor in lung volume. I work in the field of respiratory medicine and this has factor been long known to effect long volume, as well as sex, height and age.
Caucasians generally have larger lung volumes than asian and african races. You can see this in various nomograms that were published for references in pulmonary function testing. Since the age of computers we've just recently (in the last decade or so) separated the different data tables by race on a dropdown menu rather than using paper references separated by sex and race. For instance, after selecting the appropriate nomogram by sex and race, simply use a straight edge to align the height and age values and you'll get the predicted norm values.
I suspect that people with relatively more lung volume would expend less energy to stay afloat.