Thus, when people speak of "using the diaphragm" during playing, they are misinterpreting what actually happens; the diaphragm undergoes controlled relaxation during expiration and, together with relaxation of the external intercostal muscles, can only help to control the rate of emptying rather than the extent.
The external intercostal muscles which contracted concentrically to raise the rib cage during inhalation act eccentrically during exhalation as they relax and lengthen to lower the rib cage back down under control.
Thus, also stimulating external intercostal muscles or abdominal muscles is not necessary to maintain adequate alveolar ventilation in a nonexercising, paralyzed individual .
Contraction of the external intercostal muscles pulls the ribs outward, thereby preventing the inward movement of the upper rib cage; the net effect is to augment the volume of inspired air (Figure 3).
Some singers might be able to regulate pulmonary pressure for breath support through contraction of the diaphragm during exhalation (muscular antagonism); many more believe they are using their diaphragms for this purpose, but are actually engaging the external intercostal muscles.
Agonist intercostals in the parasternal region and lower external intercostals also have a large inspiratory mechanical advantage [3-4], and they contract in a predictable manner at rest [1,5].
Of the intercostal segments, the midthoracic external intercostals are best understood, and they have been found to atrophy  and hypertrophy  in clinical diseases and conditions that often occur in conjunction with chronic changes in inspiratory motor activity.