The social and economic burden of lower back pain (LBP) is very apparent in our society. It was estimated that the prevalence of absenteeism due to LBP was a massive 32% for hospital employees in Ireland (Cunningham et al, 2006).
According to a 2006 review, the total costs associated with LBP in the United States exceed $100 billion per year, two-thirds of which are a result of lost wages and reduced productivity (Katz et al, 2006).
Low back pain can arise from many different pain sensitive structures in the lower back including myofascial tissue, joint related structures, neural structures, and from the intervertebral discs (IVD) which are located between the spinal vertebrae. The IVD acts as a shock absorber, helping to absorb and distribute the load through the spine during everyday and sporting activities.
Disc degeneration has been estimated as a potential source of low back pain in 39% of cases (Helm Li et al, 2012). However it must be noted that many people have some disc degeneration and no pain as a result (Brinjikji W et al, 2015). A thorough assessment by an experienced chartered physiotherapist will be able to determine to what extent the disc may be contributing to low back pain.
Annulus Fibrosus: Comprises the tough fibrous outer layer of the disc. This tough outer layer is made from collagen fibres arranged in rings. The annulus fibrosis envelops the jelly like inner portion of the disc called the nucleus pulposus.
Nucleus pulposus: This jelly like inner layer is composed mainly of water and proteins which aid in hydration of the disc. The discs are avascular in adulthood except for the periphery, the spinal nerve supplies the area around the disc space.
In the general population it is the lower lumbar IVD’s that are more commonly affected by degeneration. As part of the normal ageing process there is usually be some disc degeneration and dehydration of the disc. This can make the IVD more susceptible to injury and sensitise it leading to development of pain in some cases.
A recent study by Belavý DL et al (2017), has shown that we are able to affect the health of our discs through exercise. Previous to this study, there is an established base of knowledge regarding loading mechanisms to avoid in order to preserve the health of the disc, namely- avoiding high compressive axial loads to the disc, flexion to the spine with compression and torque forces through the spine. These passive avoidant strategies however, will not improve the health of the disc.
Loading it :
Much in the same way we load our skeletal system to generate bone growth, it was hypothesized that the same principle may be applied to the loading of the IVD. The above study by Belavy has shown that chronic running practice in men and women is associated with better IVD composition as measured by hydration, protein content and growth of the IVD. The control group for this study were sedentary, non-active adults. The response of the IVD to running is comparable to the response of muscle to resistance training.
The current study by Belavy gives us a rough guide as to the optimum level of loading to affect the health of our discs. Total physical activity levels are not correlated with adaptation to the IVD. The most important factor in affecting adaptation to the disc was found to be acceleration (speed of movement) within a certain window. This means there is a certain speed at which optimal IVD loading is achieved. This study found that optimum acceleration (or speed) to be anywhere from fast walking to slow running or jogging.
It was found that long distance runners had the greatest growth effects to the IVD signifying the role in habitual running in the health of the disc.
The study also found there to be a ceiling effect with regards volume of training, there was shown to be no significantly greater adaptation to the IVD by increasing training volume after a certain point, much in the same way the a ceiling effect exists for muscle and bone growth.
Repetitive loading is considered to be a contributory factor in the development of lower lumbar IVD degeneration, however in this study long distance runners were shown to have better IVD hydration and protein content. From the study it can be inferred that axial loading via body weight while running is important for the health of our discs.
It is important to perform light loading activity for the health of our discs much in the same way we load our skeletal system.
By Carol O’Brien
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Katz JN: Lumbar disc disorders and low-back pain: socioeconomic factors and consequences. J Bone Joint Surg Am. 2006;21–4. 10.2106
Helm li S, Deer TR, Manchikanti L, et al. : Effectiveness of thermal annular procedures in treating discogenic low back pain. Pain Physician. 2012;15(3):E279–304.
Brinjikji W, Luetmer PH, Comstock B, Bresnahan BW, Chen LE, Deyo RA, Halabi S, Turner JA, Avins AL, James K, Wald JT. Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. American Journal of Neuroradiology. 2015 Apr 1;36(4):811-6.
Belavý, D. L. et al. Running exercise strengthens the intervertebral disc. Sci. Rep. 7, 45975; doi: 10.1038/srep45975 (2017).