Tag Archives: Abs

Ergonomics, Lower Back Pain, Musculoskeletal Injuries, The Spine, Work Place Injuries

Lower Back Pain and Spinal Loading

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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 Biomechanics. Nov;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 Biomechanics. Oct;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 Your Abs (‘6 Pack’) are Important. Part 2

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Your rectus abdominus, commonly known as your ‘6 Pack’,  has another more interesting function than those discussed in Part 1 (read my post on why your abs are important, Part 1) of this series of articles on this muscle.

Considering that the most common exercise we perform to strengthen our ‘6 Pack’ is the sit up (read my post on sit ups and lower back pain), it’s not surprising that we think the main function of this muscle is to bend ourselves double.  Few of us are though are gymnasts, thus we don’t normally use this muscle for bending our trunks, unless we’re performing situps or pikes in the gym (and if you’re picking up objects in this manner, please stop, you’re going to injure your back – another topic I’ll post about in the future).  In other words, bending our trunks is not the every day way in which we use this muscle in our daily lives.

Pike, gymnastics, rectus abdominus function
“2015 European Artistic Gymnastics Championships. Uneven bars” by Pierre Yves Beaudoin under Licence CC BY 4.0

What then is the more important function of the rectus abdominus (‘6 Pack’) in our lives? To understand more, we need to have another look at how this muscle is built.

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The ‘6 Pack’ is a long muscle that extends from the lower few ribs and inserts into the top of the pelvis.  Because we think of it as a long muscle, we think of its main function as bending us in half.  What we forget, however, is that the muscle is ‘tethered down’ by tendinous tissue giving us the ‘6 Pack’ distinctive look (when it’s not covered by blubber as mine currently is).

The important effect of these tendinous tethers along the length of the rectus abdominus is that, far more important than making your abdominal area look really ‘fit’, these tethers create stored spring like (elastic) energy in the abdominal area when you contract this muscle.

6 Pack, Abs, Rectus Abdominus
Image by Pixabay under Public Domain
Rectus Abdominus, 6 Pack, Abs, Abdominal Anatomy
“Abdominal Wall” by Henry Gray (1918) Anatomy of the Human Body under Public Domain

The stored elastic energy that is created when you contract your rectus abdominus is helpful in many ways during everyday life.  Firstly, it helps increase our intra-abdominal pressure, which is important in coughing, vomiting and emptying our bowel and bladder.  People who have been extremely unfortunate to suffer a spinal injury and no longer have function of their rectus abdominus (‘6 Pack’) can testify to how difficult it is to cough or forcefully exhale without this muscle’s function.  They often have to resort to external means such as leaning forwards or using their arms to press into their abdominal area to help replicate the function that our rectus abdominus normally performs for us.

It’s also important to understand that you don’t need to bend over to contract this muscle.  We are all able to contract our rectus abdominus while remaining upright.  This type of static contraction is called an isometric contraction.

In terms of sport and exercise though, this elastic energy also adds force and power to movements that occur at our hips or shoulders in activities such as throwing something (e.g. javelin throwing) or tennis serving or springing forwards as a sprinter and many many more examples.

Javlin throwing
“Bregje Crolla during Europacup 2007” by Erik van Leeuwen under GNU Free Documentation License.

The next question to ask then is, how am I training this muscle? Am I training it in a one dimensional capacity (e.g. performing sit ups or pikes), or am I training it in a functional way that will enhance my sporting performance.  Remember:  what you train, is what you get!

Reference:

McGill S. (2010).  Core Training: Evidence Translating to Better Performance and Injury Prevention.  Strength and Conditioning Journal, 32 (3), 33-46.

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Why Your Abs (‘6 Pack’) are Important? Part 1

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I’m intrigued by the ‘6 Pack’.  Not the one that sits in the fridge, but rather the one that joins your rib cage to your pelvis.

From my experience, I have the impression that people focus on their ‘6 Pack’ quite a lot in the gym.  As a physio, I have some reservations regarding how much people focus on their rectus abdominus (abs) as well as some of the exercises people engage in to work this muscle, since some of these exercises can actually be detrimental to spinal health (read my post on sit ups and lower back pain).

However, the 6 pack is a part of our body and it is important.  The point is, how important?  What does do your abs do for you?  What happens if you over work your abs, or if your abs are weak or damaged?  In my blog I’m going to explore this muscle in more detail in future posts.

6 Pack, Abs, Rectus Abdominus
Image by Pixabay under Public Domain

Our starting point needs to be where your abs (‘6 Pack’/ Rectus Abdominus) are found in your body and what their basic function is.

Let’s start with where your abs are found.  If you look at the illustration below, you will see that the ‘6 Pack’ extends from the rib cage to the pelvis and is found in the front of the body, in the area commonly known as the ‘trunk’.

Rectus Abdominus, 6 Pack, Abs, Abdominal Anatomy
“Abdominal Wall” by Henry Gray (1918) Anatomy of the Human Body under Public Domain

What are the basic functions of your abs (‘6 Pack’) ?  What does it do for us?

1.  Your abs/ ‘6 Pack’ help to form the front boundary of your trunk, keeping your abdominal contents from falling out.  Quite an important job I would suggest – nobody wants stomach contents gurgling around their waist as they walk.

2.  In addition, when you contract your  abs/ ‘6 Pack’, the force of this muscle increases the internal pressure in your abdominal cavity (the area below your diaphragm and lungs and above your pelvis).  You use this increased pressure when you cough, laugh, empty your bladder and bowels, vomit (nice) and forcefully exhale.  All in all, important activities at specific times in our daily lives .

3.  We also use our abs/ ‘6 Pack’ to help us sit up from a reclined position, especially when our hands are not available to help us push up.  Mothers are very familiar with this particular function, especially when they’re getting up after lying down with a sleeping baby in their arms.

4.  Contracting your abs/ ‘6 pack’ also helps you to perform impressive gymnastic maneuvers such as the headstand ‘pike’ in this video.

Pike Headstand by Carl Paoli.  Used with written permission.  http://www.nakaathletics.com/

5.  Furthermore, on a superficial level, your abs are often used as a tool when looking for a mate.  Nothing shouts fit and healthy quite like lean, muscular abs.  Don’t believe me?  Take a walk along the beach, watch people in the gym, or watch the latest Calvin Klein ad.  That should assuage any doubt.

6.  Lastly, your abs/ ‘6 Pack’ is involved in your core muscle activation and its affect on producing/reducing lower back pain.  Since 80% of us humans are going to suffer from lower back pain in our lives, it might be worthwhile to understand how our stomach strength and exercises are helping or hindering us in this matter.  I will look at this more in a future post.  Want to read more?  Read my post on Why Your Abs are Important Part 2.