Should we fear lumbar flexion/extension?

Howdy,

If you’ve spent much time in the world of rehabilitation or fitness, you’ve likely been drilled by the “neutral” spine concept. The concept of the neutral spine is that there is a specific position of the spine where it is safe from injury – particularly, from the dangers of lumbar flexion or extension. Generally, when we discuss spinal flexion and extension, there are two main types of activities that come up within the discussion: lifting with a flexed (or extended) spine (i.e. deadlift/squat…) and curling-type movements (i.e. sit-ups, leg raises, back extension variations…). Most often, there is an argument against these for their increased risk of injury.

The basic question is whether you are at less risk for pain/injury if you minimize the flexing movement of the lumbar spine during activities and if minimize the flexed position when lifting heavy…

Would we see a dramatic difference in the prevalence of low back pain if suddenly the world attempted to minimize lumbar flexion during sports, exercise, lifting, sitting, picking up their kids…?

Great research by great biomechanists (Stu McGill, Jack Callaghan) have documented a potential disc injury mechanism for repeated spinal flexion under low load in in-vitro models. Meaning, if you want to damage a disc, you’d better add some repetitive flexion and extension. 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. Static and repetitive (cyclic) lumbar flexion-extension and the associated repeated stretch of the various viscoelastic tissues (ligaments, fascia, facet capsule, discs, etc.) causes micro-damage in their collagen fibers followed by an acute inflammation, triggering pain and reflexive muscle spasms/hyper-excitability. Continued exposure to activities, over time, converts the acute inflammation into a chronic one, viscoelastic tissues remodeling/degeneration, modified motor control strategy and permanent disability. 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 are often linked with injury. A neutral spine is often associated with a more hip dominant movement strategy which may be beneficial for performance in many activities. 

When in a flexed state the active support network of the erector spinae muscles, multifidus, latissimus dorsi, and quadratus lumborum are in a stretched position, which reduces their ability to produce force to resist further deformation of the spine. This can increase the risk of the spine being moved into a position that it can’t tolerate well, spraining a ligament or fascial tissue and potentially lead into more pain than a turtle slap fight.

Based on the anatomy of the lumbar spine, we seem to suggest that it should not rotate (limited structural ROM). Instead the thoracic or hips should rotate (they have more). But we also suggest that the lumbar should not flex too much or often. This makes little sense based on the anatomy. If the thoracic should rotate because they have more of this motion then so should the lumbar flex more as it has more anatomically in comparison. The lumbar whilst having limited rotation has around 60 degrees of flexion. If having more means that it is designed to do more of it then this also needs to be applied.

An often-forgotten part of spinal research is simply looking at the available range of motion available to the spine. The lumbar spine has a great propensity to flex and extend, with up to 14 degrees of movement available per vertebral segment in the lower sections. This means there’s inherent mobility in flexion that if not trained could be lost.

Let’s talk a bit about lumbar flexion, as it’s something that brings more attention compared to lumbar extension… Spinal flexion movements help drive nutrients and promotes posterior disc hydration which may confer a positive protect mechanism against disc degeneration (a positive healing mechanism for the disc). …Dynamic spinal flexion/extension exercises are superior to isometrics for abdominal muscle hypertrophy.

Flexion movement of the spine strains the layers of collagen in the spinal discs. But, when loads on the spine are small, movement is healthy. We often recommend the cat‐camel motion exercise taking the spine through an unloaded range of motion. Thus, there is a time and place for flexion motion. When the spine loads are high in magnitude with repeated flexion motion, the collagen fibers delaminate in a cumulative fashion. Slowly the nucleus of the disc will work through the delamination and create a disc bulge. The greater the load, and the greater the repetitions, the faster this will occur.

Sure, there’s research showing that spinal flexion under load is a major predicator to injury, especially if there’s shear forces or torque applied to the spine when in a flexed position, and much of the research is coming from Dr. Stuart McGill, whose work I reference quite a bit. The forces acting on the spine increase by up to 10-15 times by simply flexing the lumbar spine, which could mean a small weight could surpass the tissues strain tolerance and lead to mechanical failure, otherwise classified as an owie.

But, beyond the need for it in activities of daily living and sports, lumbar flexion offers benefits to the spine that may not be achieved through a neutral position. Holm & Nachemson found that the intervertebral discs had increased aerobic metabolism in the outer parts of the annulus and nucleus pulposus following spinal movements. Lumbar discs rely on two main transport processes for nutrition: fluid flow and diffusion. Fluid flow is increased in flexed postures and helps to deliver nutrition better than a neutral position. In addition, a flexed posture reduces the stress at the apophyseal joints, which may be irritable from excessive extension activities. Does this indicate a better position? Not necessarily, but it may be in some instances. We know for sure, though, it is not something we need to fear.

A big component of the spinal flexion debate that is often misplaced is the role of loading during flexion. If you were to simply slump at your computer screen, the load on the low back wouldn’t be too great. Sure, it would take a toll if you stayed there for an extended period of time, like 8 hours a day, 5 days a week for the next 20 years, but to simply slump once won’t kill you. We’d be pretty poorly designed creature if all it took was a simple flexion to break us down. Furthermore, for mundane and low load tasks, involving a small amount of spinal flexion to bend and pick up stuff is more energetically efficient than using the hips or knees, which means less work is needed. Flexion is a natural and important characteristic of the spine, which means it has to be involved in order to be maintained.  

Did you know that the Kettlebell 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 1000s 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. “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. 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 deadlift ever, does their spine stay in neutral or does it typically flex more?). The compressive strength of the entire disc and vertebra unit is stronger in neutral postures. …Low load flexion (e.g bending to pick up a ball, leaning over a chair, prolonged sitting) could certainly pose much less of a risk for injury/pain when comparing ballistically picking up an extremely heavy object with a fully flexed spine.

Either repeated flexion or flexion and compression under rapid loading is required for disc herniation. Clinical and exercise recommendations recognize that many people will perform thousands of sit-ups in their lives, will flex their spine under load with abandon and will not have pain.  It is assumed that they adapt and they have a spine that tolerates bending. However, we can’t guess who has this ability so it is not unreasonable to look at solely at this research and think that the safest bet may be to avoid repeated flexion and compression.

There are studies that demonstrate sit-ups cause no more or less injury than any other abdominal exercises. All exercises carry a risk of injury and pain and this is usually from doing too much too quickly and this is no different for push-ups, squats, sit-ups…

Veres et al (2010) showed that a neutral spine is not wholly protective against disc damage.  This is significant when we recall the earlier work of Callaghan and McGill (2001) suggesting that repeated flexion-extension is a mechanism for disc herniation. These papers suggest that flexion-extension is not the only mechanism to create herniation and maintaining neutral isn’t sufficient to prevent a disc herniation under certain conditions.

The work of Gooyers et al (2015) suggests that a neutral spine is not protective of other injuries, and the loads where failure occurs are comparable between neutral and flexed position. What the data suggest is that even if lifting heavy loads and you attempt to minimize your injury risk with a neutral spine you can still damage structures (in In-Vitro models) at comparable compressive loading regardless of whether you avoid flexion. So, neutral is not wholly protective but perhaps there is a trend that flexion is still more injurious.

We see lots of spinal flexion even when trying to squat lift.  We see between 45-52 degrees of flexion.  This is comparable to what we saw in the Potvin and McGill (1991) paper that first looked at shear values in stooped versus neutral postures.  Even in those lifters who tried to maintain neutral we say more than 40 degrees of flexion. There’s a tremendous range of motion available to the spine, and to avoid using it would be analogous to not move other body parts through their full range of motion.

While we can advocate avoiding the sit-up for many reasons (performance choices being one) the alternatives may not even better when you compare the loads on the spine. As we mentioned, did you know that the Kettlebell swing will see an average of 26 degrees of lumbar flexion? The point being, if you are concerned about spinal flexion under load it may be impossible to avoid. We see that kettlebell swings, squats, jumping, skiing, running, golf, throwing, kicking, sitting etc. all take the spine to the end of its neutral range. The flexion movement that was documented to create a disc herniation might be almost unavoidable even in the tasks we are advocating instead of sit-ups (by the way, sit-ups provide a favorable risk to reward ratio…).  We could even expect that amount of load and that amount of flexion to occur in almost every sedentary individual who sits, walks, lies down, puts their shoes on, takes their socks off etc. So, we have to ask. How common are herniations. Does everyone have them? Disc herniation is estimated to be involved in low back pain 2-5%.

Herniations with neural compromise are better at explaining leg pain but quite poor at explaining back pain. However, in other papers we see a slightly different story.  Disc herniations alone aren’t related to pain but herniations with neural compromise are better related to pain. Meaning pain becomes more about sensitivity rather than damage.  We can have the damage but its only painful if there is sensitization.  This is why so many other variables influence pain – because so many other variables influence sensitivity. Therefore, our recommendations to avoid postures that lead to an assumed greater degree of loading may have little influence on the pain prevalence.

The repeated flexion and repeated loading may be a good thing for the spine and the disc. It’s not infinite and we can’t measure people’s tolerance and adaptability so we are a bit in the dark here.  This one is clinically tough.  Because we really don’t know how much flexion might be a good thing and how much might be sensitizing.  This is obvious an individual limit and would be difficult to predict.

Few facts on herniation:

• Discs can herniate even in neutral;
• Other structures can be damaged even in neutral;
• Some studies suggest that ultimate compressive strength is not influenced by flexion;
• The amount of flexion movement documented to create herniation may be unavoidable during many activities;
• Disc herniations may poorly explain the prevalence of low back pain. The disc can adapt to flexion.

People have changes on their MRIs and other imaging but it is quite often poorly linked with pain. Disc herniations can also resolve on their own and nor do herniations explain back pain very well. Heck, people have surgical repairs of their herniations, re-herniate in the future and don’t have pain. 

Many variables influence the rate of the herniation process. For example, the shape of the persons disc influences whether the herniation will be focal (Yates and McGill, 2010) and responsive to McKenzie types of rehabilitative exercises, or not (Scannell and McGill, 2009). These responsive discs are predominantly limacon‐shaped. In contrast, ovoid discs survive twisting cycles better. The thickness of the spine also influences the rate of gradual herniation – thicker spines have higher bending stress and herniate faster with flexion cycles. Further, time of day influences the rate of herniation. After rising from bed, the disc nucleus’ are fully hydrated and have much higher stresses during flexion. It is riskier to train repeated bending earlier in the morning. Occupational studies have shown avoiding flexion motion in the morning reduced disabling workplace backpain (e.g. Snook et al, 1998). Different spines mean different injury mechanisms, different resiliencies to motion, and different training approaches. Choose your parents (disc geometry and thus stress patterns came from your parents), then choose your best way to train!

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…

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 biomechanics 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.

There are those who claim that their sport is flexion movement‐based and they must train flexion movement – such as jiu‐jitsu athletes. They claim that they were not able to train because of the back pain they induced over time training flexion movement cycles. With no pain‐free capacity to train they were finished. They changed the training from a flexion movement to a flexion moment approach, thus regaining pain‐free spine flexion ability but saving the spine flexion for the ring and octagon. Their capacity to train was restored. Again, some careers were salvaged and indeed flourished.

We need to look does the person have episodic back pain, or chronic pain or perhaps has never had pain. If they are a grand master of powerlifting and have never had back pain, I suggest keeping their style. But if they have a pain history, the answer is different. First, if the spine is under load, it is best to not move it – keep it stiff. But if the spine must flex such as a strongman event competitor lifting an atlas stone? Don’t worry, the spine is stiffened in an isometrically flexed spine posture (not ideal but…). The stone is hooked by the thighs, arms and pectoralis muscles as the spine curls over the stone. The spine does not move as the motion is focused about the hip joints until the final “hoik”. So, the spine is flexed while under load but it does NOT move. The worst technique would be to move the spine into flexion, over and over, so the combination of load with motion would slowly and cumulatively delaminate the disc collagen.

After reading the information presented above, most people would likely still side with the argument that neutral is better than flexion or extension. We aren’t about to start saying that it’s best to always go with flexion; the evidence doesn’t show that. However, there are definitely situations in which flexion is both necessary and advantageous, as we mentioned above…

So, in closing, don’t fear spinal flexion/extension, just don’t load it up (especially when mixed with full range of motion). You need it to do simple thing like tie your shoes, see your shoes, get out of bed, have fun while you’re in bed, and a whole bunch of other things, so make sure you can still use it for the rest of your life. Train it, and don’t get mad at me if your discs explode when you try to do a max effort good morning with your spine at the end of its’ natural limits. Keep the loading light! …Read more below!

PRACTICAL RECOMMENDATIONS

• Avoid spinal flexion exercises within first hour of waking or after long periods of sitting. Avoid heavy lifting in general within first 2-3 hours of waking… After rising from bed, the disc nucleus’ are fully hydrated and have much higher stresses during flexion. It is riskier to train repeated bending earlier in the morning (particularly avoid maximum strength training right after waking up, it should past at least 2-3 hours on your legs – not sitting all the time). Occupational studies have shown avoiding flexion motion in the morning reduced disabling workplace backpain.
• When loads on the spine are small, movement is healthy. We often recommend the cat‐camel motion exercise taking the spine through an unloaded range of motion (it’s safe for most people even if includes end ranges). Thus, there is a time and place for flexion motion. When the spine loads are high in magnitude with repeated flexion motion, the collagen fibers delaminate in a cumulative fashion – creating a disc bulge. The greater the load, and the greater the repetitions, the faster this will occur. The worst-case scenario is when load is heavy and moves include end ranges.
• Dynamic spinal flexion/extension exercises are superior to isometrics for abdominal/back muscle hypertrophy. Sit-ups provide a favorable risk to reward ratio. This means if you want six-packs – you need to include movement.
• Repeated Low Load Activities: Suggestion – NO flexion/extension 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/extension in these cases.
• Repeated flexion/ext.-based activities: Suggestion – NO flexion/extension fear (but, of course, I completely respect the opposite view). 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. Same things go with repeated spinal flexion under load (not too much load for sure, which is something you would feel as a discomfort). There are just too many sports and activities that have this movement that it just seems unavoidable and the potential injury seems to contribute to only a small percentage of low back pain cases.  So, to exclude the sit-up seems unnecessary. However, there are plenty of other reasons to avoid it. Surely there are better exercises than the sit-up, if we are talking about sports performance (not “six packs”). 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/extension Related Pain. Suggestion: Avoid flexion/extension – at least temporarily! This is the easiest one.  If it hurts don’t do it.  Calm shit down, build shit back up.  If you have patients who consistently aggravate their pain with flexion/extension related activities then this is the time to start training neutral.  Or if they are in sports that require high degrees of repeated flexion/extension then “sparing” the spine during their training is absolutely important.
• Heavy Load Activities. Suggestion: Try to maintain neutral!
• If someone feels pain, there are some steps I like to use: Other considerations besides pain history would include findings from an assessment. I would assess the geometry of their hip joints, their function, and ability to perform clean basic movement patterns. Then I would perform provocative testing to identify the mechanism of pain generation. If the pain is resulting from flexion/extension/rotation/side bending motion, or flex./ext./rot./side b. motion when combined with a specific compressive load, there is no option regarding the training strategy that will allow the continuation of pain‐free training – painful moves must be avoided. Then I examine lifestyle and the rest of the training program. For example, if the individual sits at a computer as an occupation, most likely the training program will need to address the consequences of long duration spine flexion first. Then, together we identify the training goals of the individual, assess their current status, and decide on the best exercise tools to take them to the goal.
• If you are interested in spinal flexion/extension moves, start by not using max loads through a compromising range of motion, and try using some low to no resistance movements: cat-camel (as we already mentioned). Once you can get the range of motion with minimal loading, you can add in a couple of variables to challenge the control of the movement, like speed, instability, and variability of the surface: med. ball back rolls to standing, rolling thunder (Dean Somerset – YouTube)… From there add in some loading within the tolerances of the spine: reverse crunch, double Turkish get up…
• We need to look does the person have episodic back pain, or chronic pain or perhaps has never had pain. If they are a grand master of powerlifting and have never had back pain, I suggest keeping their style. But if they have a pain history, the answer is different. First, if the spine is under load, it is best to not move it – keep it stiff. But if the spine must flex such as a strongman event competitor lifting an atlas stone? Don’t worry, the spine is stiffened in an isometrically flexed spine posture (not ideal but…). The stone is hooked by the thighs, arms and pectoralis muscles as the spine curls over the stone. The spine does not move as the motion is focused about the hip joints until the final “hoik”. So, the spine is flexed while under load but it does NOT move. The worst technique would be to move the spine into flexion, over and over, so the combination of load with motion would slowly and cumulatively delaminate the disc collagen.
• There are many arguments on Jefferson curls… In my opinion, it’s useful to bend the spine under load every now and then (aforementioned reasons), but be careful – too much load (especially under end ranges) could be detrimental, particularly in this and similar moves where shearing forces are very high.

• The superman exercise has been shown by McGill to produce up to 6000 N (over 1300 lbs.) of compressive force to the spine due to the activity of the back extensors! McGill has shown that exercises like “superman” and the classic Roman chair back extension exercise produce excessive amounts of compressive loads on the lumbar spine. But, I wouldn’t say these are dangerous exercises even if doing with improper technique – because one can do them the entire life and never feels pain, but there are simply better options out there from both health and performance standpoint (why would we risk?). The “McGill big 3” (curl-up, side plank, bird-dog) for core stability are good choice in every sense, as well as many other exercises.

For the love of movement,

Luka