Re: Who has a greater lung capacity a 9 year old boy or a 9 year old girl?

Thanks for your question.

I didn't find data that compared children directly by age. They typically compare children by size; more specifically, lung volume (typically called total lung capacity, TLC, or the total amount of air you can fit in the lungs while they are still in the chest) in boys and girls are compared by height.

Lung capacity is closely correlated to a person's overall size. A girl who is taller and/or heavier than a boy of the same age could easily have a larger lung capacity than that boy. Girls also enter puberty earlier; in America, age 9 is a common time for girls to enter puberty. Boys enter puberty a bit later than girls. A girl that has then grown significantly taller at 9 years of age than her male counterpart is likely to have a larger lung volume. This is because chest and lung volume grow much faster during puberty than the steady, gradual growth that occurs before puberty. On average, however, when boys and girls of the same height are compared (not considering their age), boys have slightly larger lung volumes. The TLC of boys' lungs is about 3-5% larger than that of girls of the same height. Although girls have slightly less overall volume when compared by height, one study found that girls had superior air flow when lung volumes of the same size were compared between Caucasian girls and boys.

So to answer your question more directly, we'd have to compare boys and girls by age, or know how much taller girls were at 9 years old than boys. That's different for different countries and even different cultures within the U.S., so the answer may change depending on what population of people we're examining. I didn't find any studies that did that comparison. There is, however, some basic, trustworthy, educational lung material at the American Lung Association at http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=710069

Tim Nicholls, MD
Berkeley, CA

References:
Stocks J, Quanjer Ph.H. Reference values for residual lung volume, functional residual capacity and total lung capacity. ATS Workshop on Lung Volume Measurements. Official Statement of the European Respiratory Society. Eur Respir J 1995; 8: 492. Available at http://www.erj.ersjournals.com/cgi/reprint/8/3/492.pdf

Neve V, Girard F, et al. Lung and thorax development during adolescence: relationship with pubertal status. Eur Respir J 2002; 20: 1292. Available at http://www.erj.ersjournals.com/cgi/content/full/20/5/1292

Rosenthal M, Bain Sh, Cramer D, Helms P, Denison D, Bush A, Warner JO. Lung function in white children aged 4 to 19 years: I--Spirometry. Thorax 1993; 48: 794.