Is it safe to load and stress the discs in our back?
Written by Mitchell Robinson
1) Changes in our discs only have a very weak association with pain!
- When we scan backs for research we find that a large portion of the population have what we would consider damage and/or degeneration in their backs without pain. As we age, the discs in our back also age - and this is completely normal! We don't only exhibit changes on the outside (wrinkles, grey hair etc.), we also exhibit changes on the inside. Sometimes we call these changes in the spine 'wrinkles on the bones' or 'grey hairs on the inside'.
Figure 1. Imaging findings from Brinjikji et al (2014) of spine degeneration present in high proportions of asymptomatic individuals, increasing with age.
Implications: We have treated the human body like a car, building or machine (ie., a purely structural thing) for too long. This approach has failed us. There seems to only be a weak association between physical changes (as seen on imaging) and pain states.
Image 1. Lumbar spondylosis (umbrella term for spinal degeneration).
2) Findings on scans are not predictive of future episodes of back pain
- A 10-year longitudinal study found no relationship between the degenerative changes to intertebral discs and future complaints of back pain. (Tonosu et al., 2017)
Implications: It's common to hear (from well-meaning poeple) something like, 'you may be okay now, but your back will pay for it later'. It seems this belief is context dependent (ie., not necessarily true).
3) Discs need some load and movement to keep them healthy
- The discs in our backs have a tough outer ring (annulus fibrosus) and an inner gelatinous part (nucleus pulposus) which is ~80% water. This creates a kind of water cushion providing the disc with a shock-absorbing ability and allows it to be deformable. The discs don't have blood vessels throughout them. Instead, they get their nutrient delivery and waste removal via fluid moving in and out as we load and unload them. (By the way, something similar happens in the meniscus in the knee!) The pumping action causes diffusion and convection (fluid flow) in and out of the disc which actually improves disc health. Movement and loading is essential for a happy healthy spine!
Image 1. Your discs are like sponges; fluid moves in and out in response to compression and decompression.
Implications: We have demonised something that's actually very important for back health - namely, loading and bending it! Our backs love weights (think deadlifts and squats), walking and running. Moreover, if it's true discs like compression and decompression, what's wrong with slouching? Sitting in a flexed position for a bit isn't horrible for you! In fact, sitting in a relaxed position helps fluid resorption to a greater extent than sitting upright (Pape et al., 2018).
4) Loading the discs promotes a regenerative process!
- The discs of runners are better at "binding water" (absorbing and holding water in them) (Belavy et al., 2017). Moreover, the discs in cyclists also seem to be bigger and healthier than their sedentary counterparts. They exhibit more glycosaminoglycan content meaning their discs hold more water and act as better shock absorbers (Belavy et al., 2019). So much for the harm in sitting for long periods of time in a flexed position!
Implications: Your back is not like a stack of cards; a very fragile thing that can easily fall apart. Your back is an extremely strong structure that can handle huge amount of bending, twisting and loading!
5) Being inactive means you'll have more degeneration over time, not less!
- Sedentary individuals show a greater loss of disc height, more fat in their back muscles and more low back pain than their active individual counterparts (Teichtahl et al., 2015). These results have been corroborated in another study showing more pronounced degenerative changes in inactive people over a 14 year period (Maurer et al., 2020).
Implications: You are not like a car or building - a purely structural thing. Humans are a little more complicated than this! When you expose a building to environmental stressors it slowly breaks down. When you expose a human body to stressors over time it slowly builds up! So, get up and get moving!
Final thoughts: There's obviously a limit though! It's possible (or course) to do too much! You need to find the right amount of activity for you. Don't do too little and don't do too much; some call this finding the Goldilocks amount.
(It should be said we feel like that's worrying about a ditch on the other side of a mountain. In other words, our problem is that we are too inactive as a society rather than too active.)