Final answer:
The abdominal muscles and the serratus posterior inferior muscles are integral to forced breathing and the Valsalva maneuver, aiding in bodily functions such as respiration, defecation, and childbirth.
Step-by-step explanation:
The abdominal muscles and serratus posterior inferior muscles play a critical role in forced breathing, also known as hyperpnea. This type of breathing is evident during vigorous activities such as exercise or when an active manipulation of breathing is necessary, like in singing. During forced inspiration, the scalenes and other neck muscles contract to lift the thoracic wall, increasing lung volume. Conversely, during forced expiration, the abdominal muscles, including the obliques, forcefully contract and the internal intercostals help compress the rib cage, both actions aiding in decreasing thoracic cavity volume and expelling more air.
In addition, these muscles perform other important functions such as aiding in forceful bodily processes like defecation, urination, and childbirth. These actions often involve the Valsalva maneuver, a cooperative effort between the diaphragm and abdominal musculature. This process not only aids in respiration but also plays a role in the stabilization and increase of intra-abdominal pressure that facilitates these forceful bodily functions.