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's 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), 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 voluntary movements of the limbs. The diaphragm role in trunk stability occurs simultaneously with its 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

Trunk stability can be achieved through the coordinated effort of the muscles known as the core musculature. Due to their location, the core muscles form a box. The front of the box consists of the abdominal muscles. The back of the "box" includes global and local stabilisers. The top of the box is the diaphragm and the pelvic floor muscles are the bottom of the box. Co-contraction of the diaphragm, pelvic floor and abdominal muscles creates a rigid cylinder which decreases the load on the spine.

Spinal stabilisation is provided by the global and local muscles. Global muscles create power and large movements, while the local muscles provide stability by connecting the pelvis and ribcage to the spinal fascia. To achieve and maintain spinal stability, the local muscles must contract before the global muscles. In addition, the pelvic floor muscles and diaphragm add to trunk stability as part of the local muscle system.

Local Muscle System

The local muscle system has 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: This important muscle properly places the abdom­inal contents and helps support the lower back. It increases spine stiffness during functional posture and movements.
• Multifidi: Considered a primary stabiliser of the spine as it controls intersegmental spinal motions. It controls precise movement and provides inter-spinal stability. Evidence points to the multifidus muscle being continuously active in upright postures. This muscle stabilises the vertebrae as the spine moves.
• Internal Oblique: Helps maintain abdominal pressure and movements of the trunk along with the other muscles. It provides stability by connecting the pelvis and ribcage to the spinal fascia.
• Deep transversospinalis: The erector spinae muscles play an important role in spinal stability.

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: involved in overall stability and mobility by creating power and large movements
• External oblique: generates torque and general core stability
• Rectus abdominis: raises intra-abdominal pressure during contraction and helps to maintain posture during trunk movement
• Quadratus lumborum: involved in trunk stability in the sagittal, frontal and horizontal planes

The Diaphragm

The diaphragm is a primary muscle of respiration. It is a local stabiliser. It separates the abdominal and thoracic cavities and increases intra-abdominal pressure.

The diaphragm originates at:

• the sternal part originates from the xiphoid process of the sternum
• the coastal 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

The point of insertion of the diaphragm is the central tendon.

The diaphragm is innervated by the phrenic nerves (C3-C5).

Pelvic Floor Muscles

The pelvic diaphragm is a wide but thin muscular tissue layer forming the inferior border of the abdominopelvic cavity. Composed of a broad, funnel-shaped sling of fascia and muscle, it extends from the symphysis pubis to the coccyx and from one lateral sidewall to the other. The pelvic diaphragm is part of the local stabilisers. These muscles maintain trunk stability by improving intra-abdominal pressure. This is accomplished by co-contracting with the transverse abdominis, multifidus, and diaphragm muscles.

• Levator Ani Muscle (pubococcygeus aka pubovisceral, pubovaginalis, puboanalis, puborectalis, iliococcygeus)
• Coccygeus
• Piriformis
• Obturator internus
• Arcus tendinous of the levator ani
• Arcus tendinous fasciae pelvis

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.

This video explains the concept of respiratory pump, where the pressure alteration in the thoracic and abdominal cavities during inhalation and exhalation compresses or decompresses the inferior vena cava.

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." Patients present with observable signs and symptoms that indicate disruption of the spinal stabilisation system.

Interventions

• 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.
• Trunk stabilisation exercise to improve balance
• 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)
• Three progressive stages of exercises to improve spinal stability:
  • Isolated, conscious activation of the local muscles
  • Activation of local muscles during movement of the limbs
  • Local muscle system activation during daily activities
• Technique to improve segmental spine stabilisation, including abdominal drawing-in manoeuvre (ADIM):
  • Patient in the supine position, with their hip joint flexed to 40 degrees and knee joint to 80 degrees
  • Instruct the patient to pull the navel deeply to the lumbar region.
  • The patient maintains contraction while breathing lightly

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

Additional Resources

• Core Strengthening
• Diaphragmatic Breathing Exercises