What Can Be Learned from Crocodiles

Unlike many lizards, crocodiles possess a muscle akin to the human diaphragm known as the Diaphragmaticus. This muscle attaches to the hip joint, encasing the pelvic girdle. Importantly, it connects to the liver, which in turn links to the lungs. When a crocodile inhales, the diaphragmatic muscle contracts, pulling the liver toward the tail, thus increasing thoracic volume and facilitating air intake. Crocodiles also utilize other major muscle groups for respiration, including intercostal muscles, core muscles (rectus and transversus abdominis), and muscles that assist with pubic bone rotation to enhance inhalation and expand lung capacity (Munns, 2011).

The coordinated movement of the liver during inhalation, along with its elastic rebound during exhalation, allows crocodiles to move and breathe simultaneously. This ability to create internal volume and engage secondary respiratory muscles is absent in lizards. Humans, much like crocodiles, must also create space to increase thoracic volume. Mastering this synergy is key to the rhythm of our voice, making it essential to maintain this capacity.

Sadly, this capacity is often diminished, especially when stress triggers a regression to lizard-like breathing patterns. Such regression, guided by neural mechanisms shared with reptiles and activated by the autonomic nervous system in response to threats, can lead to a decreased ability to breathe effectively. While life continues, it is akin to running an engine on fewer cylinders than available—resulting in compromised vocal quality. A quivering voice under pressure exemplifies reduced breath capacity and disrupts the harmony between voice and breathing musculature.

The Physics and Biology of Voice Production

The diaphragm plays a pivotal role in voice production. With each inhale, approximately 500ml of air enters the lungs, which can increase significantly. On average, about 2 liters of air remain in the lungs, and it is impossible to fully deplete them.

The phrenic nerve, originating from the cervical spinal roots (C3, C4, C5), is essential for diaphragm movement. It is the sole motor supply to the diaphragm, a dome-shaped muscle situated beneath the heart and lungs. The visceral pleura, a membrane surrounding each lung, connects to the diaphragm, meaning any diaphragm movement influences lung function.

When inhaling, the diaphragm flattens, while abdominal muscles allow the organs to shift down and outward, creating space. This movement increases thoracic volume, similar to crocodiles, enhancing breath capacity. The diaphragm consists of two domes connected by a central tendon, with one dome positioned higher due to the liver. Its connections to the lower rib cage, xiphoid process, and lumbar vertebrae can surprisingly affect breathing efficiency and voice quality.

To unlock vocal potential, it is vital to release any unnecessary tension in the abdominal muscles, which can restrict diaphragm movement. Muscle tightness often arises from stress-induced responses, leading to lingering tension that hampers breathing.

The Role of Ribs in Breathing Mechanics

The intercostal muscles, aided by the lattisimus dorsi, elevate the twelve rib sets, allowing for lung expansion. Ribs near the spine are bony but become more flexible as they approach the front of the body. The design of the thorax allows for downward and outward movement, increasing volume as one descends the body.

Floating ribs, which connect solely to the vertebrae, are often overlooked in discussions of thoracic capacity. When free to move, they swing outward, and maintaining this freedom is crucial, given the diaphragm's attachment to the lumbar spine.

The ability to manipulate internal space, like crocodiles, presents endless possibilities for bodily movement and adaptation, a trait humans have utilized throughout history.

Breath as the Driving Force of Voice: The Myoelastic-Aerodynamic Theory

The air we breathe is essential for vocalization; without a continuous airflow, vocal folds cannot achieve the necessary vibration for speech. The voice consists of countless air pulses, each shaped by the vocal tract to produce desired sounds. Air is propelled upward through the trachea by controlled contractions of respiratory muscles, simultaneously closing the vocal folds and trapping air beneath them. This creates a pressure imbalance, forcing air through the folds, resulting in sound production.

Voice intensity can be amplified by increasing lung airflow and adjusting vocal fold resistance. The vocal folds can be drawn apart and held open longer, enhancing sound amplitude. Additionally, the rate of opening and closing determines voice pitch, typically around 110 vibrations per second during normal conversation.

What Happens When Problems Arise

The Myoelastic Theory of Phonation is an energy-efficient means of speech production, relying on air pressure dynamics. However, speaking can still lead to fatigue or throat soreness.

Maintaining the ability to adjust and create internal volume is crucial for effective communication. Our emotions and their expression are directly tied to our breathing patterns. In stressful situations, we may feel choked or find our words escaping us. Stress triggers a survival response that can neglect the biological mechanisms required for efficient breathing and speech.

Elevated shoulders during inhalation, often a sign of anxiety, indicate reliance on secondary breathing muscles instead of primary ones, leading to increased effort. Similarly, a locked abdomen can restrict diaphragm movement, compromising rib expansion. To compensate, neck and shoulder muscles may engage, creating a habit that affects voice quality.

It's essential to inhale adequately for effective communication. For many, anxiety is a constant presence, making it vital to understand how stress affects the body and to relearn efficient breathing methods.

In conclusion, inhalation should expand the rib cage in all directions, not just elevate the chest. Allowing the belly to rise indicates that the organs are making room for diaphragm descent. Embracing this natural movement, rather than tensing the abdomen, can significantly preserve vocal quality. The floating ribs and lumbar region should also experience expansion. When these muscles work harmoniously to support vocalization, one may discover newfound confidence and a connection to the crocodile's mastery of breath.

Appendix

The Rib Cage & Intercostal Muscles

The rib cage consists of seven true ribs connected to the sternum, three false ribs attached to the spine, and two floating ribs. Anchored to twelve thoracic vertebrae (T1-T12), two sets of intercostal muscles—internal and external—run between each rib. The contraction of external intercostals lifts the ribs, expanding the rib cage, while the internal intercostals decrease its size.

Works Cited

Farmer, CG & Carrier, David. (2000). Pelvic aspiration in the American alligator (Alligator mississippiensis). The Journal of Experimental Biology, 203, 1679–87.

Heinrich, B. (2002). Why We Run: A Natural History. Ecco Press.

Munns, L., Owerkowicz, T., Andrewartha, Sarah J., & Frappell, P. B. (2011). The accessory role of the diaphragmaticus muscle in lung ventilation in the estuarine crocodile Crocodylus porous. The Journal of Experimental Biology, 215, 845–852.