|MadSci Network: Anatomy|
This is an excellent question - you worked out an interesting science experiement and have used the data to think about what might be happening. That's great science!
One of the problems you may be having in getting information is that 'lung capacity' in referred to as 'vital capacity', an old-fashioned phrase from the idea that breathing is 'vital' (as in 'vitatlity'). I found some data on the web that you can compare with your data. Unfortunately all the data was on adults - you will have to do a little searching of your own if you want data on children's lung capacity (or 'pediatric vital capacity'). The web sites where I found this information are listed at the bottom of this page, and I have also listed a favorite book you may want to look at if it is in the library.
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. I think lung capacity decreases with age because of a decrease in the stretchiness, or elasticity, of the lungs, but I may be wrong - physical fitness may play a part, too. 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)).
If you think about the lungs in a child growing as the child grows, it is clear that lung capacity increases as the size of the lung increases. So we would expect that lung capacity is larger in bigger people. Here is the equation in adults: women (7.63 - (0.112 x age)) x (height in centimeters), men (21.78 - (0.101 x age)) x (height in centimeters). This also takes into account the change in age, but is only for the decrease in lung capacity in adults. It wouldn't work for the increase in lung capacity in children up to 18 years old.
Physical fitness does change lung capacity. Unfortunately again, most information on lung capacity and fitness that I found on the web was part of an advertisement, so the information was not trustworthy. (If the person who tells me that something is Really Important is the same person who gets my money, I don't tend to believe that person.) You can go to the national library of medicine to get information about lung capacity (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi), but these papers are usually hard to read. Instead, the Center for Disease Control and Prevention (http://www.cdc.gov/health/default.htm#L) and the National Insitutes of Health (http://health.nih.gov/search_results.asp) usually have trustworthy information that is easier to understand.
Genetics also plays a factor. The March 30, 2003 "Observer" had a story about sherpas, Tibetan people who live high on the mountains, which said that they have bigger lung capacities.
http://faculty.washington.edu/kepeter/119/labs/ vc-females.htm and http://faculty.washington.edu/kepeter/119/labs/ vc-females.htm
You may find the information onf this site useful, http://www.riverdeep.net/science/biology_gateways/bg_overview s/catn.ovw_SPG .jhtml especially the pdf on lung http://www.riverdeep.net/science/biology_gateways/bg_handouts/rsp/rspt n5i.p df
Berne, R. M. and M. N. Levy (editors). 1998. Physiology, 4th edition. Mosby, Inc. St. Louis, MO.
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