Breath is vocal power! Without airflow, the body can not produce voice.  Held tension patterns and facial restrictions can decrease respiratory range of motion.  This affects generation and coordination of pressure and airflow which directly affects voice quality, stability, and vocal phrasing.

Breath is not generated by the lungs. Aside from elasticity, the lungs are passive.

When we inhale, pressure is primarily generated by the diaphragm muscle and is affected by connected muscles including the hip flexors (psoas and iliacus) and the QL. Expiratory pressure is primarily generated by the abdominal muscles. Both inspiratory and expiratory pressure are also generated by the many muscles and connective tissue acting on the ribcage as well as the elasticity of the lungs and ribcage .

Based on individual wants/needs, breathwork may begin with manual addresses all muscles of respiration including diaphragm release, hip flexor release, and all accessible respiratory muscles