How is that for a title?

A major concern of strength coaches, physiotherapists and other health care professionals is teaching people to NOT bend their spines when they lift things. It is assumed that spinal flexion is an independent risk factor for low back injury and pain. For a detailed review please read here

The point of this short post is to consider the ramifications of the cadaveric animal models that investigate spinal loading and injury mechanisms and how this might inform clinical practice.

Background

One of the strongest arguments against spinal flexion are the numerous in-vitro (meaning dead animals) studies that look at what happens when you repeatedly bend and load a disc/motion segment. Numerous studies (here, here, here and here) have shown that loading a spinal motion segment when it is out of neutral appears to be more injurious to the disc than if you just loaded the disc in neutral.

So, if you are biomechanist it would seem that its a slam dunk on one thing to recommend to prevent low back pain. Try to keep your spine in neutral when you go to load it. But, there are some issues.

1. The advice doesn't seem to work. We have been giving that advice for years and low back pain is still quite common. See an older review here on a biomechanical analysis of stoop v. squat lifting
2. Many would say that those are DEAD spines. They can't adapt like humans would to load. That if we took a dead tendon out of a cow and pulled on it repeatedly that the tendon would fail - and no one would then argue that we should avoid loading tendons. (we don't by the way, we load tendons appropriately to have them adapt).

We now have a professional REACTION based on these arguments. Those who are challenging the conventional wisdom of avoiding spine flexion and are arguing that it is irrelevant for injury/pain. Many would say we should ignore the in-vitro work because it is flawed. I would not go that far and wanted to put forward another way to view this research

MORE BACKGROUND - Two Observations from the vast literature

Observation #1: In-vitro animal models don't load repeatedly to End ROM

In the animal model studies they bend the spine varying degrees. Some work suggests that the amount of spine flexion is just to the end of the neutral zone which may be about 35% of max end ROM (Gooyers et al 2015 and Callaghan & McGill 2001) and other studies suggest it is more (not explicitly stated but it looks to be about 60-70% of max end range Wade et al IIRC)

UPDATE: While the Callaghan and McGill (2001) paper did write that the amount of flexion was 35% of max this might be an underestimation. The max value was achieved by bending the segment until it fractured. This is not something you do when testing functional max flexion. Other papers from the lab with similar models (e.g pig spines) suggest that the max flexion was probably around 22 degrees. And since the motion segments were flexed around 17 degrees that means that the % of max flexion was about 77%. This doesn’t change the argument too much since this is still the amount of spine flexion seen in many sports and ADLs.

Observation #2: Spinal Flexion is Unavoidable during lifting, bending and squatting

We typically measure spinal flexion as the difference in flexion of the sacrum versus the amount of flexion at L1 by devices that are strapped to the skin above those joints. Numerous studies have shown that even when people try to maintain a neutral or lordotic spine they still have large degrees of flexion (typically greater than 20 degrees which is often more than 40% of max flexion). Here are some examples below:

1. Kettlebell swings showing an average of 26 degrees of flexion

2. Good morning exercises showing between 25-27 degrees of flexion

3. Squats and deadlifts showing 50% and 80% max flexion respectively (soon to be published MSc out of University of Saskatchewan with Scotty Butcher)

4. "Lordotic lifting" postures showing around 30 degrees of flexion when the trunk is only tilted 65 degrees forward. Even when people tried not too flex they still flexed. (See slide below)

5. Laura Holder (2013) showed the exact thing as Arjmand 2005. Take a look at the picture and note how it looks neutral but it is flexed still.

So what is my point?

Alright. Here we go. The in-vitro studies do not stipulate that it is only end range flexion that is injurious. Many just go to the end of the neutral zone (which seems to be different across studies). The amount of flexion used to create a disc injury at times seems to be as little as 30% of max ROM. (note: it is a hard to give a definitive answer for this because what is reported is the absolute amount of spinal flexion for a motion segment rather than how much it can move maximally). In the lumbar spine this seems to be around 15-18 degrees for the entire spine motion.

What is so interesting to me is that it seems like it is IMPOSSIBLE to avoid this amount of lumbar flexion. Meaning people will regularly squat only to parallel and have 50% of max flexion or do a beautiful Kettlebell swing with around 50% of max flexion too. Deadlifting or lifting from the floor is even more (80% of Max Rom according to Scotty's work). Just look at the above picture - she looks in neutral with no flexion and we have 22 degrees!

My point (finally) is that both sides of this debate could be correct.

Meaning, the in-vitro spine models COULD be valid. Spinal flexion could be risk factor for disc damage. But, there might be little point in being concerned about it because it is impossible to avoid and hold on...disc degeneration is an absolutely normal and unavoidable part of being a human and is poorly related to pain! Meaning we get worried about disc degeneration contributing to pain but it might be just a tiny drop in the pain cup (not irrelevant but just kindling for a fire. ). Thus, don't worry about that little drop in the cup but worry about all the other factors that might be more important.

Potential and Practical Take Home Points and Opinions (one way to look at this)

1. Symptom Modification: If spine flexion hurts then you can certainly change it a little bit. So, let symptoms be your guide in how you move sometimes. Temporary avoidance might be the right answer for some people some of the time (I'd also say its wrong for some people and they need to expose to flexion but that is another blog)

2. Use other factors/goals to when making biomechanical decisions. Meaning tweak your biomechanics for performance, to shift stress or to target different muscle groups or movements depending on your goals.

3. Follow good training principles when it comes to training and loading your spine - Don't do too much, too soon, dumbass.

4. Maybe don't freak out so much about spine flexion. Recognize that it is a normal part of movement and other variables are probably more important for pain

5. Maybe we just avoid or minimize heavily loaded, full range lumbar spine flexion. Not because there is specific research on the spine but because we do this with other joints as well.

6. Again, similar to all joints maybe we should vary our spine postures during a number of tasks. Meaning, if load management is important perhaps being able to lift, bend, squat, sit, row and flip with a variety of positions is the best way to balance the application of stress with the required time to rest and recover. So maybe movement quality just means you can move anyway you like. And perhaps Preparation trumps Quality.

*I know these practical points are good because people on both spectrums of the debate will agree with some and disagree with others. I've made no one completely happy.

Reconciling spinal flexion and pain: we are all doomed to failure but perhaps it doesn't matter