Bill Hartman On Controlling Your Abdominal Muscles During Respiration by Muhammad Amir Ayub

As the title goes:

The influences of gravity and our anatomy establish a path of least resistance of airflow to the lower front of the lungs and ribcage. Your ability to exhale effectively is dependent on your ability to expel the air from this area.
It is the abdominal muscles that strongly influence how well you move air out of the lungs and ribcage. As you complete the exhale and the ribs move downward, you’ll feel the abdominal muscles become active and firm.

Relaxing the abdominal muscles gives up control of lower ribcage, and it refills with air upon the next inhalation.
The abdominal muscle should be active to control the rib cage but not restrictive to inhalation. Without control of the lower rib cage, the upper and back portions of the rib cage cannot expand with air. This may limit your ability to reach fully overhead (airflow to the upper ribcage is required) or bend forward (airflow to the back of the ribcage is required) without compensating around a limitation.

Don't think that this is quackery. Medically, those with high spinal injuries have ineffective respiration and coughs as the spastic yet paralyzed (loss of control) abdominal muscles restrict ribcage movement, leading to loss of lung volumes on inspiration and the ability to actively exhale during coughing. Check out the video too in the link.

(And that concludes my recent flurry of posts. I was just too busy.)