The chief causes of flabby abdominal muscles, with its consequent low intra-abdominal pressure, are a sedentary life, the wearing of corsets which prevent the free play of the abdominal muscles, and the overdistention of the abdominal walls by repeated pregnancies and by the accumulations of fat.
As a result of lax abdominal walls, there is very frequently an enteroptosis or a falling of the abdominal contents far below their normal position; this includes the liver, spleen, pancreas, the intestines and stomach, and is the most frequent cause of floating kidney.
Further, the accelerating influence of the diaphragmatic movements on the circulation is seriously interfered with.
The Importance of Good Chest Development.—The least chest development of the adult woman—that is, the underarm girth around the chest—consistent with good health is 28 inches, and this girth must be enlarged 3 inches on forced inspiration. In ordinary respiration the waist expansion should be from ½ to 1 inch, while during muscular activity it should be from 1½ to 3 or 4 inches.
In women the movements of the upper part of the chest are very conspicuous, the breast rising and falling with every respiration; whereas, in children and in men the movements are almost wholly confined to the lower part of the chest, and are called diaphragmatic, in contradistinction to those seen in women, which are called thoracic. It is now the opinion of many observers in this country and in Europe that the habit of thoracic breathing in women has been brought about by constricting the waist and the lower ribs. Observations made among the Indians and Chinese women show that the abdominal is there the type of breathing, and civilized women who wore no corset had relatively good abdominal breathing. Further, that a thoracic type of breathing can be produced in man by putting him in a corset.
Vital capacity is, as we have seen, the term employed to denote the amount of air that can be expired after the fullest possible inspiration. The amount for persons 5 feet in height has been estimated as 174 cubic inches, with an increase of 8 cubic inches for every inch in height above this. The relation between height and vital capacity is rather remarkable, since height is chiefly determined by the length of the legs, and not by the size of the trunk and thorax. This is due to the fact that mobility of the chest increases with stature.
The capacity of the chest is determined by the spirometer. A person who can only blow, say from 180 to 250 cubic inches, has a good pair of lungs, while, on the other hand, an ability to blow only 100, even where percussion and auscultation had revealed nothing, is suspicious.
One test by the spirometer is not sufficient to judge of the condition of the lungs, since the woman may be nervous or may not understand how to breathe into it, so that a number of tests should be made on different days, which may give a much better result, though no change has occurred in the lungs.
Proper relation between the height, weight, and chest measurement:
| Height. | Average weight. | Average chest measurement. | |
| Feet. | Inches. | Pounds. | Inches. |
| 5 | 120 | 29.80 | |
| 5 | 1 | 122 | 30.60 |
| 5 | 2 | 125 | 35.00 |
| 5 | 3 | 128 | 35.75 |
| 5 | 4 | 131 | 36.25 |
| 5 | 5 | 135 | 37.00 |
| 5 | 6 | 139 | 37.50 |
| 5 | 7 | 143 | 38.00 |
| 5 | 8 | 147 | 38.50 |
| 5 | 9 | 151 | 39.00 |