Article by Simon Bell
The debate concerning whether or not to bend using spinal flexion is a long and hotly contested one. My personal opinion on this has changed several times over the course of my career which is a good thing. It means new evidence is coming to light all the time that changes the complexion of the conversation. That's how science should work! This blog addresses current evidence surrounding the topic and what the best course of action should be for back pain sufferers.
Neutral Spine:
The idea behind using a neutral spine (i.e avoiding bending or favouring a squat motion when lifting) stems from several different sources. The main idea is it reduces the load borne by the posterior elements of the spine (the bits at the back) such as the facet joints that in theory, are a bit too weak to cope with high loads over time without sustaining damage. A second aspect in support of staying ‘neutral’ stems from the work done by McGill and colleagues regarding repetitive loading and spinal disc injuries. Simply put, the amount of times our discs can cope with repeated bending without sustaining damage is limited. So the idea goes, if you can limit the amount of back bending you, limit potential disc damage. McGill & Callaghan (2001) showed disc injury is more likely caused by low load repetitive flexion than heavy lifting (exposure occuring little and often). Wade et al. (2015) have shown an increase in the likelihood of disc injuries compared to end plate injuries at lower loading rates. From repeated bending, you are more likely to get a disc injury than a vertebral one.
A further aspect to strengthen this argument is the apparent link (stemming from a academic bunch of papers) between a phenomenon called ‘ligamentous creep’ and spinal flexion. Basically, there are physical changes that occur within the spinal ligaments under repetitive or constant flexion load that can potentially cause instability in the lower back and lead to injuries.
A further point of support for this idea is the relationship between an increase in compressive loading, anterior shear force and back injury. It’s pretty much established that bending forward causes an increase in shear forces, or sliding forces, between the vertebrae which of course increase if you’re lifting heavy objects. However, some researchers have recently suggested these forces, when combined with compression at least, can link to a greater increase or the risk of injury even with no extra load (so, simply by bending rather than squatting).
There are other reasons you can find to back up the idea of squatting when lifting, or at least not bending over all the time. However, they all pretty much amount to the same idea: that repeated bending and not keeping a ‘neutral’ spine can lead to spinal injury.
So, What Is There to Argue About Here?
Well first off, there’s the relationship between this focus on not bending and a previous blog I wrote on the topic of fear avoidance. Briefly, this is a common process whereby the body protects itself when exposed to a perceived threat. This can be pretty much anything; I’ve seen patients suffer with this from tying a shoe, brushing their teeth, deadlifting 200kg and everything in between! Where this links to bending and squatting is the psychological fear that comes with pain and the association of specific movements with triggering a pain episode. For example, if you have suffered from back pain while bending, it’s possible you could become fear avoidant when bending over in the future – known in the trade as flexion intolerance.
There is an argument here that suggests patients who have suffered back pain and are avoiding bending out of fear are at risk of damaging their recovery simply by avoiding further bending.This is especially interesting when given the low percentages of genuine clinically definable spinal injuries when looking at overall back pain statistics. Some studies have suggested as low as 10% of all back pain is directly attributable to disc injury. Therefore, it might be a better course of action to teach patients to become conditioned to all forms of movement rather than fearful of a particular type!
From a more mechanical point of view, there have been some solid and extensive studies which have provided less than convincing results regarding clear links between full flexion/bending and spinal disc damage. Veres (2010) tested the failure rates of discs in different positions including neutral and flexion by basically pressurising them until they failed. The results showed several interesting things, including the notion that flexion may reduce posterior disc herniations like the ones that press on nerves! It is theorised that the disc fibres at the back stretch when pressurised in a flexed position which gives them strength against pressure going backwards. So, potentially safer than a neutral spine?! The study also showed internal disc damage is worse in a neutral spine and with rapid load versus gradual which is oppositional to the MgGill studies (2001).
Kingma et al. (2010) also showed some interesting stuff when looking at the same areas. They compared people squatting with people bending to lift boxes. Not only did they show there is less sliding force present when lifting something normally than when trying to keep a neutral spine, but that it might even be pointless to try! As part of their study, they measured the actual degree of flexion present in the back between all types of lifting technique with the stats reading only slightly different between bending vs neutral spine squats! This means your back will still bend even when you try not to!
Ultimately, the situation is more complicated than whether it's better to squat or bend! There’s a fantastic article by Greg Lehman called ‘Revisiting the Spinal Flexion Debate’ that examines each of the reasons in detail and it's definitely worth a read.
So, What Does This All Mean?
Well, it's pretty clear there’s no hard and fast rule with this stuff. As the papers above show, day to day activities will always involve some back bending. So, it’s probably not a great idea to keep trying to avoid it unless you currently have back pain and sensitivity. Having said tha,t it’s probably true that with higher forces and heavier weight come greater demand on the spinal segment. It may be more efficient and back sparing to reduce bend when there are high forces present. One of the most important points in all this though is that the link between disc damage and back pain is generally pretty poor. With the amount of flexion we do day to day being mostly unavoidable, there’s a pretty good chance most of us already have some level of damage but aren’t suffering as a result and disc damage may even have the potential to heal of its own accord (which is good news, of course!)
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