Understanding Flat Back Syndrome

This detailed Muscle and Motion article, will provide a comprehensive review of Flat Back Syndrome and explore effective ways to diagnose and conservatively treat this condition.

Understanding flat back posture:

Flat back, or fixed sagittal imbalance, refers to a postural spinal imbalance or deformation in the sagittal plane where the normal lumbar lordotic curve is reduced. This condition affects the spine’s natural alignment and can have functional implications. Normally, the spinal curves, including cervical lordosis, thoracic kyphosis, and lumbar lordosis, provide benefits such as reducing skeletal loads, increasing range of motion, and improving balance by aligning the center of gravity on the support base of the legs.

In a flat back posture, the lumbar lordotic curve is decreased compared to the norm, leading to a greater posterior pelvic tilt and a smaller lumbosacral angle than usual. The lumbosacral angle is formed by the connection between the spine and the pelvis, specifically between vertebrae L5-S1, and typically measures around 40 degrees.

A faulty flat back position has a noticeable lumbar lordosis flattening, a prominent posterior pelvic tilt, and a reduced lumbosacral angle. This can result in a straight appearance of the lower back, even though the pelvis may be in a normal neutral position.



What causes a flat back?

The term ‘flat back syndrome’ has been broadened to encompass any patient who exhibits symptoms resulting from a reduced inward curvature of the lower spine.

Other potential causes and risk factors associated with flat back syndrome include:

  • Congenital: Flatback syndrome can also be present from birth (congenital), where a baby is born with an underdeveloped vertebrae.
  • Harrington rod procedure, which is a spinal fusion treatment for scoliosis, is often associated with Flatback syndrome. This procedure can result in various issues such as compensatory effects, degeneration of nearby discs, difficulties with standing, disability, and persistent back pain.
  • Degenerative disc disease: Conditions such as ankylosing spondylitis and rheumatoid arthritis can contribute to the development of a flat back syndrome.
  • Vertebral compression fractures: Osteoporosis can lead to fractures in the vertebrae, affecting the spine’s alignment and resulting in flatback syndrome.
  • Lumbar post-laminectomy syndrome: After undergoing a laminectomy for spinal stenosis, some individuals may experience flatback syndrome as a complication.


Why does flat back posture contribute to back pain? 

It is crucial to note that not all cases of flat-back posture result in back pain. The causes of back pain are multifaceted and cannot be attributed solely to a single factor. Instead, they involve a complex interaction of biological, psychological, and social factors that vary from person to person. These factors are not mutually exclusive and can influence one another. Let’s dive into the mechanical theory behind flat-back pain:


  • Impaired shock-absorbing mechanism of the spine: 

The spine’s natural curves help absorb shocks during dynamic activities like walking, running, and jumping. In flatback posture, this mechanism is compromised, disrupting the shock absorption process and the appearance of back pain symptoms.

  • Limited spinal mobility during flexion: 

In normal forward flexion, the lumbar curve integrates with the thoracic curve, allowing for a greater range of movement. However, in flatback posture, there is limited mobility and range of movement in the lower back (L1-L5 vertebrae) due to the absence of a continuous arch and integration of curves during flexion. This results in sagittal movement with large levers, increasing the load on the axis area and contributing to back pain.

To learn more about this, see the video on testing the continual arch.

  • Increased pressure on the intervertebral discs in the lower back: 

The intervertebral discs in the lumbar spine serve as shock absorbers. However, in a flat-back posture, the anatomical structure of the spine is altered, causing increased pressure on the intervertebral discs. 

Want to learn more about reasons that may contribute to flat back and back pain? Check out our video about Reasons for back pains in flat back.

How to diagnose flat back 

A comprehensive medical history should be obtained to accurately diagnose flat back posture to identify any underlying causes that may contribute to this condition. During the physical examination, it is important to assess the spinal curvatures in various positions, including lying down, standing, sitting, or bending. Special tests such as Adam’s forward bend test and Schober’s test can provide additional information regarding the degree of curvature. If flat back posture is suspected, X-rays or other imaging tests might also be conducted to measure the extent of the curvature and rule out any other underlying conditions. These diagnostic procedures help to confirm the diagnosis and guide appropriate treatment options.


Common characteristics of flat back: 

Common muscular characteristics observed in individuals with flat back posture include

  • Anterior and posterior pelvic tilt rigidity in the sagittal plane.
  • Tight hamstrings, contributing to posterior pelvic tilt.
  • Weakness in the hip flexor muscles leads to lengthening and weakness in the muscles involved in anterior pelvic tilt, such as the iliopsoas and rectus femoris.



Treatment of flat back:

Based on these characteristics, exercises for individuals with flat back posture may include:

  • Exercises to improve overall mobility of the lower back vertebrae.
  • Stretching exercises explicitly target the hamstring muscles to promote lengthening.
  • Strengthening exercises focusing on the muscles involved in an anterior pelvic tilt.

To deepen your understanding of flat back and optimize your treatment for this condition, we highly recommend downloading our Posture APP.  Our Posture APP will provide valuable insights and practical guidance with 3D illustrations on diagnosing and treating flat back and other postural disorders. Don’t miss out on this invaluable tool to enhance your diagnostic abilities and treatment knowledge.




At Muscle and Motion, we believe that good posture is essential for your long-term health and well-being. Our Posture App can help you improve your posture and reduce pain. Sign up for free today!


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Written by Uriah Turkel, Physical Therapist and Content Creator at Muscle and Motion. Uriah’s areas of expertise are anatomy, kinesiology, sports rehabilitation, gait analysis, and rheumatology.

And Dr. Gill Solberg, “Muscle and Motion” Posture & Yoga apps Co-Founder.

Uriah Turkel B.P.T
Uriah Turkel B.P.T
Uriah Turkel B.P.T, graduated from Ariel University School of Health Sciences, Physiotherapy Department. Uriah works as a content creator specialist at Muscle and Motion, his areas of expertise are anatomy, kinesiology, sports rehabilitation, gait analysis, rheumatology, and pain neuroscience. During his first degree, he conducted research on treatment methods for chronic ankle instability and the effects of Functional Electrical Stimulation (FES) on Peroneal Muscle Function in the Neuromuscular & Human Performance Lab. Currently, he is pursuing a Master of Science at the same lab, researching cognitive and gait decline during aging.