The Role of the Diaphragm in Trunk Stability

Original Editor - Carin Hunter based on the course by Rina Pandya
Top Contributors - Carin Hunter, Ewa Jaraczewska, Jess Bell, Kim Jackson and Merinda Rodseth

Introduction

This article looks at the role of the diaphragm in trunk stability. The diaphragm role should not be forgotten when working with patients post-mechanical ventilation or in individuals with lower back pain, gait or balance dysfunction, as the diaphragm has an important role in maintaining lumbar spinal stability. This task is accomplished through increased intra-abdominal pressure (IAP), by minimising displacement of the abdominal contents into the thorax and generating tension in the thoracolumbar fascia. To stabilise the thorax, the diaphragm responds via a feedforward control system to any voluntary movements of the limbs. The diaphragm engagement in trunk stability occurs simultaneously with the ventilation function.

This article includes a brief overview of the muscles of respiration and discusses concepts that are relevant when working to re-educate the diaphragm and enhance core stability.

Overview on Muscle Systems

Local Muscle System

The local muscle system comprises a deep, slow-twitch muscle layer that controls intersegmental movements. These muscles respond to changes in posture and extrinsic loads.

Key local muscles include:

• Transversus abdominis
• Multifidi
• Internal oblique
• Deep transversospinalis
• Pelvic floor muscles

Global Muscle System

The global muscle system' involves fast-twitch, long muscles with a large lever arm to produce torque and gross movements.

Key global muscles include:

• Erector spinae
• External oblique
• Rectus abdominis
• Quadratus lumborum

For more information, please see this page: Muscles of Respiration.

The Diaphragm

Origin

• The sternal part originates from the xiphoid process of the sternum
• The costal part originates from the sixth to twelfth ribs
• The lumbar part originates from the medial and lateral arcuate ligaments, and the bodies of L1-L3 vertebrae

Insertion:

• Central tendon

Innervation:

• Phrenic nerves (C3-C5)

Action:

• Primary muscle involved in respiration
• Separates abdominal and thoracic cavities
• Increases intra-abdominal pressure

Important Concepts in Relation to Diaphragm Rehabilitation

Thoracoabdominal Pump

• The diaphragm plays an important role in venous return. On inspiration, the diaphragm descends. This diaphragm movement increases pressure in the abdominal cavity and decreases pressure in the intrathoracic cavity. Increased pressure in the abdominal cavity leads to compression of the inferior vena cava (IVC), which helps to move blood, against gravity, into the right atrium of the heart.
• The same applies to the abdominal lymph vessels. Negative intrathoracic pressure, caused by the descent of the diaphragm and compression of the abdominal lymph vessels, leads to an upward movement of the lymph. The valves in the thoracic duct prevent the lymph from flowing back down.

Valsalva Manoeuvre

• The Valsalva manoeuvre is defined as forced expiration against a closed glottis. It is associated with increased intrathoracic and intra-abdominal pressure.
• This simple movement is associated with a complex cardiovascular response and other regulatory mechanisms.
  • The primary aim of these mechanisms is to control arterial blood pressure.
• Physicians can assess arterial blood pressure and heart rate changes during and after a Valsalva manoeuvre to diagnose or confirm a diagnosis of a range of conditions.
• Detecting heart murmurs:
  • The Valsalva manoeuvre can also be used clinically to classify heart murmurs as clinically right-sided or left-sided.
• For more on this test, please see this page: Valsalva Test.

The Diaphragm's Role in Balance and Gait

The diaphragm is primarily a muscle of respiration and it controls how we breathe. However, it also has an important role in stabilising the trunk to enhance balance and walking in conjunction with the abdominal muscles and paraspinal muscles.

The Diaphragm as a Core Stabiliser

The diaphragm, multifidus, transversus abdominis, and pelvic floor muscles act as one unit at the centre of various functional kinetic chains. It has been noted that the cooperative actions of these muscles control intra-abdominal pressure, fix the trunk, and reduce stress on the spine, especially in the lumbar region.

Watch this video to understand the postural support mechanism involving the diaphragm, pelvic floor muscles and vocal cords:

Muscle of Abdominal Straining and Weight Lifting

Contraction of the diaphragm and the muscles of the anterior abdominal wall leads to an increase in intra-abdominal pressure during normal processes like micturition, defecation, vomiting and parturition (childbirth).

Trunk stability

There are two types of spinal instability:

1. Gross Instability: obvious radiographic displacement of the vertebra associated with neurologic deficit and deformity.
2. Functional/Clinical Instability: Clinical instability is "the loss of the spine's ability to maintain its patterns of displacement under physiologic loads so there is no initial or additional neurologic deficit, no major deformity, and no incapacitating pain"

• Core strength provides proximal trunk stability for distal mobility. Hence, most exercises prescribed by physiotherapists will focus on the mobility of extremities along with core/ lumbar stabilisation and deep breathing techniques.
• Training of the core involves the coordination of both sensory and motor inputs, comprising of:
  • Neuromuscular control
  • Passive structural components (osseous and ligamentous elements)
  • Active mobile components (29 pairs of muscular elements)

More information on the rehabilitation of the diaphragm is available here: Diaphragm Rehabilitation

Additional Resources

• Core Strengthening
• Diaphragmatic Breathing Exercises