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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).

(1-4,11).

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!

(3,4).

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).

 

References:

  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.
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Why the Spinal S-Curve is Important in Back Pain

Lower back pain is extremely common.  It is so common that 8 out of 10 people will experience it at some point in their lives.

Lower back pain can be caused by many factors.  These include factors such as genetics or birth defects (spondylolysis), trauma (falls or car accidents), infections (bacterial infections or even TB of the spine), and poor posture and movement patterns.  Sometimes a combination of causes is to blame for our lower back pain.  Out of all the factors I’ve listed, the one that we have the most control over on a day to day basis, is our posture and our movement patterns.

Back Pain
Personal Injury Back Pain by SanDiego’s PersonalInjury Attorney’s Photostream is licenced under CC by 2.0

The most at risk postures for developing lower back pain are sitting and bending postures.   These two postures when performed badly put our spines at a high risk of developing lower back pain, and people who do a lot of sitting and people who perform a lot bending are often the people who complain of lower back pain.  Think of office workers, drivers, nurses, machine operators, fatory workers, manual workers and more.  These people and others who engage in a lot of sitting and/or bending on a day to day basis are the people who are at risk and who do develop lower back pain.  Does that sound like most of us?  Exactly, hence the high incidence of lower back pain!

Read my post on driving postures and lower back pain.

One of the most important elements of our posture in helping to prevent lower back pain, is the s-curve of our spine and maintaining the s-curve of our spine in different postures and movement patterns.

Read my post on correct lifting posture for picking up children.

The spinal s-curve consists of 3 different curves.  There’s a curve that goes in at the neck (the cervical lordosis), followed by the curve that goes out in the upper back (the thoracic kyphosis) and the curve that goes in again at the lower spine (the lumbar lordosis).  The depths of these curves may vary in different people, but we all have the 3 curves illustrated below and they are very important for our biomechanics and general spinal health.

spinal s-curve
Vertebral Column by Unknown and is licenced in the Public Domain

The importance of these curves in helping to prevent lower back pain, is that these spinal curves throw our centre of gravity between our feet.  With our centre of gravity lying between our feet, the compressive and shearing forces on our spine which may lead to lower back pain are reduced.  Keeping these shearing and compressive forces as low as possible acting on our spine helps to keep the forces acting on our backs within limits that our body tissues can naturally withstand, which then helps to reduce or prevent lower back pain.

centre of gravity
Center of pressure in relation to centers of gravity while walking by Jasper.o.chang under licence CC BY-SA 3.0

When we change these curves through engaging in poor posture while sitting, standing, lifting, driving, picking up children etc., we increase the forces on our spine unnecessarily causing many problems with the complex spinal biomechanics and anatomy that result in injury and lower back pain.

 

How often do you lose your spinal curve in your activities during your day?  Do you suffer from back pain?  Is your poor posture partly to blame?