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).
The larger external intercostal muscles assist in inspiration when the tidal volume is large by pulling the ribs upward and outward.
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.
Additionally, single occlusions in anesthetized animals robustly facilitate the lower external intercostals to a greater extent than the diaphragm or parasternals  and thus may undergo an even greater relative muscular remodeling with ITTO.