Tag Archives: biomechanics

Lower Back Pain and Spinal Loading

Lower back pain is a very complex problem and may have many causes.  One cause is when spinal tissue failure occurs as a result of high compression forces applied through the spine leading to spinal injuries.  High spinal compression forces may lead to micro fractures in the vertebral endplates, compression fractures of the vertebral bodies and damage to the spinal discs (1-3).

Activities which cause high spinal compression forces include:

  • Lifting heavy weights.
  • Lifting lighter weights in weak postures which increase the functional weight of the object and thus the load on spinal tissues (e.g. lifting from the floor or above shoulder height).
  • Sustained spinal bending postures (with or without a load in the hand).
  • High repetition spinal bending postures (with or without a load in the hand).
  • Exposure to whole body vibration in vehicles that experience vibrational acceleration including shocks between 2-6g (11).


Certain body postures also create higher compression forces through the spine than others.  For example, bending the spine while lifting, increases the pressures on the spinal discs by more than 100%.   Spinal bending combined with twisting increases spinal disc pressures by more than 400%.  On the other hand, when people recline backwards in a chair, even while adopting a slouching posture, spinal disc pressures reduce by 50-80% – a posture most of us adopt when we’re getting tired during extended bouts of sitting.  Sitting up straight in a chair actually creates twice the spinal compression compared with reclining backwards in a chair – something to tell your granny or your teacher when they criticize your reclined slouching posture!


In 1979, it was noted that when heavy lifting was performed while holding one’s breath (for a few seconds), the intra-abdominal pressure was raised, the spinal extensor muscles activity reduced and both led to reduced compression loading on the lumbar spine, reducing the risk for spinal injury.  However, if the heavy lifts extended for longer than a few moments, the breathe was released and the intra-abdominal pressure fell to much lower levels, reducing this spinal support mechanism substantially (5).  This reduction in spinal compression due to raised intra-abdominal pressure was supported by research published in 2003, 2006 and 2010 and showed that the greatest benefit occurred when the body was in flexed (bent) postures (6-8).

The question arises as to how raised intra-abdominal pressure reduces spinal compression and helps to protect the spine from spinal compression failure leading to spinal injury and lower back pain.

Both abdominal and spinal extensor muscle contraction cause an increase in the spinal compression forces.  However, the abdominal muscle contractions (0- 40% MVC) also assist in raising the intra-abdominal pressure, and when doing so, the net forces on the spine result in reduced spinal compression.  In these circumstances it was also found that there was a reduction in the activity of the erector spinae muscles, with a greater reduction in these muscles’ activity corresponding to a greater increase in intra-abdominal pressure (8).

Furthermore, a 2013 published study revealed that chronic lower back pain sufferers who were experiencing a remission from their pain still exhibited lower levels of agonistic abdominal muscle activity and higher levels of antagonistic paraspinal muscle activity when compared to healthy individuals when performing spinal flexion (stooping/bending) with or without handling a load.  This alteration in their abdominal and spinal muscle recruitment activity/ patterns could result in increased spinal loads (not measured in their study) and possibly contribute to the recurrence of lower back pain in individuals where these altered recruitment patterns have become the norm (9).  On the other hand, research published in 2011 showed that activation of the core muscles showed no improvement in spinal stability, casting doubt on the mechanism in which core muscle rehabilitation is used to assist in the treatment of chronic lower back pain (10).



  1. Chaffin D.B.; Park K.S (1973). A longitudinal study of low-back pain as associated with occupational weight lifting factors. Am Ind Hyg Assoc J. 34(12):513-25.
  2. Freivalds A.; Chaffin D.B.; Garg A.; Lee K.S. (1984). A dynamic biomechanical evaluation of lifting maximum acceptable loads.  J Biomech. 17(4):251-62.
  3. Adams M.A.; McNally S.D.; Chinn H.; Dolan P. (1994). Posture and the compressive strength of the lumbar spine. J Biomech. 27(6):791-791.

  4. Nachemson A.L. (1981). Disc pressure measurements. Spine. 6(1):93-7.

  5. Hutton, W. C.; Cyron, B. M.; Stott, J. R.R. (1979). The compressive strength of lumbar vertebrae. J Anatomy. 129(4): 753-758.
  6. Daggfeldt, K.; Thorstensson, A. (2003).  The mechanics of back-extensor torque production about the lumbar spine. J Biomech. 36(6): 815-823.
  7. Arjmand, N.; Shirazi-Adl, A. (2006). Role of intra-abdominal pressure in the unloading and stabilization of the human spine during static lifting tasks. European Spine Journal. 15:1265–1275.
  8. Stokes I.A.; Gardner-Morse M.G.; Henry S.M. (2010). Intra-abdominal pressure and abdominal wall muscular function: Spinal unloading mechanism. Clinical BiomechanicsNov;25(9):859-66.
  9. D’hooge, R.; Hodges, P.; Tsao H.; Hall L.; MacDonald D.; Danneels L. (2013). Altered trunk muscle coordination during rapid trunk flexion in people in remission of recurrent low back pain. J of Electromyograhy and Kinesiology. Feb;23(1):173-81.
  10. Stokes I.A.; Gardner-Morse M.G.; Henry S.M. (2011). Abdominal muscle activation increases lumbar spinal stability: analysis of contributions of different muscle groups. Clinical BiomechanicsOct;26(8):797-803.
  11. Bazrgari, B.; Shirazi-Adl, A.; Kasra, M. (2008). Seated whole body vibrations with high-magnitude accelerations—relative roles of inertia and muscle forces. Journal of Biomechanics. 41:2639-2646.

How Does Lower Back Pain Work? Part I

Lower back pain is so common that 8 out of 10 us will experience it at some point in our lives.  Any person who has experienced lower back pain can testify to how debilitating lower back pain is and how much it can negatively impact on your daily life, making common gestures like picking up a tissue off the floor, nearly impossible (read my post on how to strengthen your abs when you have lower back pain).  Not only that, suffering from lower back pain is likely to make driving extremely difficult, if not even more painful (click here to read more about driving posture to reduce lower back pain).  Sitting for long periods at the office or even trying to continue with your normal sport or recreational activities are also negatively impacted when lower back pain comes to call.  All in all, one of the least desirable ailments (read my post on how picking up your children badly can cause lower back pain).

How then does lower back pain work?  Understanding something is the first step in learning to deal with it better and hopefully to help find a way to reduce it’s impact in our lives.

Broadly speaking, your lower back pain will either be mechanical in nature or inflammatory (read about inflammatory lower back pain), or a combination of these.

lower back pain
Image by LadyofHats Mariana Ruiz Villarreal under Public Domain

When your lower back pain is mechanical in nature, this means that it relates to your biomechanics and to your musculoskeletal function.  In other words, it’s how your bones, joints, muscles, nerves, blood vessels and discs are affected by your movements, postures and your rest, to either cause you lower back pain or relieve your lower back pain.

As some of you would know, often when you have lower back pain, some postures and movements are hell and others keep you sane and able to function.  

It’s important to take note when this is the case.  Some people suffering from lower back pain tend to take no notice of what aggravates or eases their lower back pain and they are missing out on very important information in helping to understand and treat their problem correctly and swiftly.

When your lower back pain is due to a mechanical cause, any movement such as sitting/rising/walking/bending/arching backwards/straightening your knee etc. will either increase, decrease or maintain the intensity of your lower back pain.  This is because the mechanical forces created by these movements will have increased, decreased or remained constant on parts of your body tissues such as your spinal discs, facet joints, muscles or nerves.

In addition, you need to understand that different structures in the body are affected by different movements and postures and the forces that they apply.  They are also affected by the type of damage that has occurred and how this causes the affected body tissue to respond to different mechanical forces.

Spinal discs for example are generally aggravated by bending and twisting and can be eased by arching backwards (in certain circumstances, in other circumstances the opposite is true – hence it’s important to see your OMT specialised Physio for assistance since they are especially trained to know these differences and much much more).  On the other hand, generally speaking, your facet joints are aggravated by arching backwards but eased by bending and twisting.  Thus, it’s really important to take note of which movements ease, aggravate or maintain your lower back pain.  This information will help your OMT Physio get to the root of your problem faster.

Next time I will discuss chemical causes of lower back pain.  Any comments?  Please feel free to post them, I would love to hear from you.