Final answer:
During forceful inhalation or exhalation, additional muscles of the respiratory system become active.
Step-by-step explanation:
During forceful inhalation or exhalation, additional muscles of the respiratory system become active. In addition to the diaphragm and external intercostal muscles, other accessory muscles are involved in forced breathing. For example, during forced inspiration, muscles of the neck and rib cage contract to increase lung volume, and during forced expiration, abdominal muscles assist in pushing air out of the lungs.