Should we allow the back to bend?

Whether the spine should flex (bend) repeatedly and under load is an old debate that we are still having having and we should be having. The basic question is whether you are at less risk for pain/injury if you minimise the flexing movement of the lumbar spine (low back) during activities and if minimise the flexed position when lifting heavy.

The case to minimise flexion is laid out in an article detailing how the Canadian Military has removed the sit-up from training. I have probably taught 1000's of people to hinge at their hips and try to minimise spinal flexion during many activities, certainly activities that demand high loads on the spine, for example: Moving & Handling techniques.

But is this right?

Would we see a dramatic difference in the prevalence of low back pain if suddenly the world attempted to minimise lumbar flexion during sports, exercise, lifting, sitting or picking up their kids? Would injuries and pain decrease if the sit-up were banned and office workers were forced to stop them from slouching in their desks?

I'm not going to criticise researchers or clinicians favouring any particular side because I've held all those positions too and nothing is black and white here.

The point of this is to try and present the two sides to this debate. My bias is still to try to avoid spinal flexion under many conditions while at the same time caring very little about spinal flexion under other conditions.

The Case for Neutral

• Stu McGill & Jack Callaghan have documented a potential Disc injury mechanism for repeated spinal flexion under low loads. Meaning, if you want to damage a disc you'd better add some repetitive flexion and extension. Also supported by the work of Wade.

• Repeated flexion is cumulative and we assume that the discs have a finite number of flexion cycles. That finite number will certainly vary across people but we can't measure someone's adaptability or estimate their tolerance

• Biomechanists have also shown that the compressive strength of the entire disc and vertebra unit is stronger in neutral postures.

• Lifting from low heights (we assume that this requires a flexed spine) can increase the prevalence of low back pain

• Spinal flexion induces ligamentous creep and influences the role of the spinal musculature. The link to pain is unknown.

• Lifting with a flexed spine versus a neutral spine leads to comparable levels of compression but increases in the amount of anterior shear. Anterior shear and cumulative compressive loading is often linked with injury.

• There is NO research showing that a flexed spine is stronger when it comes to injury or pain.

• A neutral spine is often associated with a more hip dominant movement strategy which may be beneficial for performance in many activities.

The caveat here is whether you are scaring people and creating pain expectation. An individual's spine can be robust but that doesn't mean they might not be sensitive.

Expectation: "I've been told to not flex my spine because it creates injury" can certainly sensitise some people. Expectations have been linked to poorer outcomes and greater pain.

Trunk bending is related to occupational low back pain.

Lifting from low heights can increase the prevalence of low back pain. The limitation of current research is that it doesn't measure the degree of spinal flexion. It just measures that the entire trunk was tilted relative to vertical. It is unknown if the forward bend comes from the hips, thoracic spine or lumbar spine. Only that bending forward someway is related to low back pain incidence

Neutral is the dominant view and clinical expertise has a role in guidelines, eg: Moving & Handling guidelines

Neutral is the view most espoused by experts.

The Case for Flexion

• Some studies show that disc herniation is possible even in a neutral spine. This suggests that Neutral alone is not wholly protective of other injuries and the loads where failure occurs are comparable between neutral and flexed position

• Repeated spinal flexion might be largely unavoidable. While we can advocate avoiding the sit-up for many reasons the alternatives may not even better when you compare the loads on the spine. Did you know that the Kettle-bell swing will see an average of 26 degrees of lumbar flexion. Or squatting, when trying to be in neutral, can see 40 degrees?

• Flexion in sport may also be unavoidable. Think golf (about 48% of max flexion repeated 1000's of times a day), rowing, throwing, kicking, cycling, landing when snowboarding, skiing etc. Sports which are flexion biased do not have greater degrees of low back pain versus those in neutral

• If you are worried about the loads in a sit-up or the loads on the spine when lifting with a flexed spine you need to be worried about doing everything. Neutral is not protective against loads.

• Disc herniation might be the least of our worries. Disc herniation is estimated to be involved in low back pain as low as 2-5%.

• Damage in the spine is poorly linked with pain. Loading of the spine is not very well linked with damage or degeneration. Our recommendations to avoid postures that lead to an assumed greater degree of loading may therefore have little influence on the pain prevalence.

• The body adapts: repeated flexion and repeated loading may be a good thing for the spine and the disc. Its not infinite and we can't measure people's tolerance and adaptability.

• A flexed spine during lifting is both metabolically more efficient and is often associated with greater force output (i.e. when you see someone lifting their best dead-lift ever, does their spine stay in neutral or does it typically flex more?)

Summary

I respect clinicians who take both positions on this issue. It is obviously not cut and dry. My bias through the years has been to go Neutral especially under heavy load conditions and I would stay with that recommendation for many reasons, the least of which being injury risk. I would suggest that performance goals and symptoms should drive our clinical and movement strategies. I will break the suggestions down into different scenarios.

Repeated Low Load Activities

Suggestion: No flexion fear

These are things like bending over to tie your shoe, fluffing your pillows, sitting etc. The spine can handle bending. Its built for it. Don't freak out over flexion in these cases.

Repeated Flexion based activities

Suggestion: No flexion fear

If you love doing sit-ups, have done them for years and you don't have low back pain I would be hard pressed to tell someone to stop doing them. To exclude the sit-up seems unnecessary. However, there are plenty of other reasons to avoid it. Surely there a better exercises than the sit-up?

If you are starting a training program and the sit-up can't be justified based on performance goals then why would you do it? And if you have flexion related pain then.

Flexion Related Pain

Suggestion: avoid flexion - at least temporarily

This is the easiest one. If it hurts don't do it. Rest and rebuild your activities up gradually! If you have patients who consistently aggravate their pain with flexion related activities then this is the time to start training neutral. Or if they are in sports that require high degrees of repeated flexion then "sparing" the spine during their training is absolutely important.

However, there maybe cases where other "impairments" are relevant. For example, you might work with a rower who is consistently aggravated by repeated flexion. When looking at their rowing technique they appear to be more flexed than their team mates. They might also have less hamstring flexibility than average. Here you have a person who is sensitized to flexion, whose sport requires flexion and whose physical parameters dictate that they need more spine flexion to do their functional task. None of those previous factors are inherently injurious or faulty but under certain circumstances they contribute to the sensitivity. Addressing them in the person is relevant but might not be in an individual under different circumstances.

Heavy Load Activities

Suggestion: try to maintain neutral

Even though some research suggests that flexion may not be worse than neutral there is no research showing it is safer. High load activities are examples where bio-mechanics are important. We are dealing with loads that might exceed the structural strength of the tissue. Psychosocial variables may have a smaller or non-existent role to play here at least with the injury mechanism. I'm comfortable choosing the Neutral position here. You can also justify this based on performance with many high load activities and high performance activities being associated with a hip dominant movement strategy.