Yoga for Breath Support for Speech 69Consequently, air enters the lungs until the two pressures equalize
(Seikel et al. 2000).
In contrast to quiet inspiration, forced inspiration requires the
activation of the external intercostal muscles, which are located
between the 12 pairs of ribs in the thoracic cavity. These muscles
provide mobility and unity to the rib cage. The external intercostal
muscles are considered accessory muscles because inspiration
can occur without them. However, by elevating the rib cage, the
external intercostal muscles significantly increase the quantity of
air inhaled into the lungs. Other accessory muscles that contribute
to forced inspiration reside in the thorax, as well as in the neck,
shoulder, and arm regions of the body (Seikel et al. 2000).
During quiet expiration, the diaphragm relaxes and ascends,
decreasing the volume of the thoracic cavity and concomitantly
increasing air pressure. Consequently, air flows out of the body
until the pressure between the lungs and the atmosphere equalizes.
Three passive forces, namely torque, elasticity, and gravity, drive
the exhalation phase of breathing by restoring the respiratory
system to a resting position. First, torque, the rotary restoration
force, unwinds the cartilages adjacent to the sternum that twist
and elevate during inspiration. Second, the porous, highly elastic
nature of lung tissue, which stretches during inspiration, facilitates
return of the lungs to their original size and shape. Third, gravity
pulls the ribs back to rest in both standing and sitting positions
(Seikel et al. 2000).
In contrast to quiet expiration, forced expiration requires
musculature to act indirectly on the lungs to “squeeze” air out of
them. As the rib cage is elevated during inspiration, the internal
intercostal muscles, the innermost layer of the intercostals, and
the transverse thoracic muscles are activated to depress the rib
cage. In addition, several abdominal muscles contract to compress
the abdomen and move the internal organs, such as the intestines,
in an upward direction. This reduces the size of the thorax (Seikel