The diaphragm is commonly understood as a breathing muscle. What is less widely appreciated is that it is simultaneously one of the primary stabilisers of the lumbar spine. Research by Professor Paul Hodges at the University of Queensland demonstrated that the diaphragm contracts in anticipation of limb movements, a feedforward mechanism that pre-stiffens the trunk before forces are generated. This stabilising function depends on the diaphragm working in coordination with the pelvic floor, transversus abdominis, and multifidus to create and regulate intra-abdominal pressure. When any of these structures is dysfunctional, the whole system is compromised.
How Posture Impairs Diaphragm Function
The diaphragm is a dome-shaped muscle that attaches to the lower ribs, the thoracic and lumbar vertebrae, and the sternum. Its optimal function requires the rib cage to be in a neutral position, neither excessively flared nor compressed. In forward head posture and thoracic kyphosis, the rib cage is compressed anteriorly, the diaphragm's mechanical range of motion is reduced, and the muscle is forced into a less efficient excursion pattern. Research using ultrasound imaging has confirmed that diaphragm excursion is significantly reduced in individuals with thoracic kyphosis compared to those with neutral thoracic alignment. The clinical consequence is both reduced breathing efficiency and reduced spinal stabilisation capacity.
Signs of Diaphragmatic Dysfunction
- Breathing with the upper chest and accessory neck muscles rather than the lower ribs and abdomen
- Inability to generate intra-abdominal pressure under load, sometimes presenting as inability to brace effectively for heavy lifting
- Recurrent low back pain worsened by breathing or by movements that require trunk stability
- Pelvic floor dysfunction, as the diaphragm and pelvic floor must act as coordinated pressure regulators
- Frequent sighing, which indicates chronic over-breathing and low CO2 tolerance
- Sensation of not being able to get a deep breath even in the absence of respiratory disease
Restoring Diaphragmatic Function
Diaphragmatic breathing rehabilitation begins with awareness. Lying supine with the knees bent, place one hand on the lower ribcage and one on the upper chest. Breathe so that only the lower hand moves on the inhale, tracking the lateral expansion of the lower ribs. Once this pattern is established in supine, it should be practised in sitting, then standing, then during movement. Research by McGill and colleagues at the University of Waterloo demonstrated that diaphragmatic bracing, in which the diaphragm descends and intra-abdominal pressure rises on inhalation before a load, significantly reduces shear forces on lumbar discs compared to conventional abdominal hollowing techniques.
Nutrition and the Diaphragm
Excessive visceral adiposity directly impairs diaphragmatic excursion by elevating the resting position of the diaphragm and reducing its downward range of motion. Research has documented significant improvements in diaphragm function following weight loss in obese individuals. Magnesium deficiency impairs smooth muscle function including the respiratory muscles, and adequate magnesium is relevant to respiratory efficiency. Vitamin D receptors are expressed in respiratory muscle tissue, and deficiency is associated with reduced respiratory muscle strength in multiple studies.
Sources
- Hodges, P.W., & Gandevia, S.C. (2000). Activation of the human diaphragm during a repetitive postural task. Journal of Physiology, 522(1), 165-175.
- Kolar, P., et al. (2010). Postural function of the diaphragm in persons with and without chronic low back pain. Journal of Orthopaedic and Sports Physical Therapy, 42(4), 352-362.
- McGill, S.M. (2015). Back Mechanic. Backfitpro, 2nd edition.
- Shirley, D., et al. (2003). Spinal stiffness changes throughout the respiratory cycle. Journal of Applied Physiology, 95(4), 1467-1475.
- Bordoni, B., & Zanier, E. (2013). Anatomic connections of the diaphragm: influence of respiration on the body system. Journal of Multidisciplinary Healthcare, 6, 281-291.