During normal growth body proportions change appreciably. The skull increases comparatively little in size. The legs grow proportionately more than the trunk. Prader (lower figure) recorded the change in the relationship between ratio of legs and sitting height in Swiss children and adolescents. Sitting height represents the distance from buttocks to cranium in a seated person; it comprises the head, neck and abdominal area and is therefore not a simple token for the height of the thorax. At any rate it is obvious that during growth the legs constitute an increasing proportion of the standing height. Not until the adolescent growth spurt do body proportions tend to stabilize.
The lungs are contained in the thorax, a part of the trunc. As body proportions change during growth it should not come as a surprise that the relationship between the volume of the lungs and standing height is subject to change. Changes in body height are therefore less than ideal for scaling lung growth.
Understanding is better than plain knowledge. So let us have a look at the skeleton.
Fig. 1 modified from: Thomas A McMahon and John Tyler Bonner: On Size and Life. Scientific American Books, Inc., New York. ISBN O-7167-5000-7. Fig. 2 modified from: Prader A, Largo R, Molinari L & Issler C (1989). Physical growth of Swiss children from birth to 20 years of age. Helvetica Paediatrica Acta Suppl. 52, 1– 125.