Flexion relaxation response & low back pain

There is a growing body of literature exploring the EMG activity differences of the trunk muscles between individuals with low back pain and without. Each study trying to determine: if EMG differences exist, if they differ depending on the cause of low back pain, if EMG activity is a reliable objective measure for low back pain, and if treatment changes these EMG levels. 

When I first heard of these studies I had wasn't entirely sure how EMG studies related to my clinical assessment of LBP or how I was able to measure EMG levels in the treatment room? It wasn't until I took at master class with Rob Laird, Specialist Musculoskeletal Physiotherapist from SuperSpine (Melbourne), that I began to understand how it all fits together. If we were to measure EMG activity it would tell us not about strength of lumbar erector spinae muscles, but of the activation patterns

I first met Rob in 2013 during his masterclass on the assessment of the lumbar spine. At this point in my career, I had be introduced to the O'Sullivan Classification for non-specific LBP and Rob spoke about this model as a part of his clinical practice but also introduced me to the flexion relaxation response (FRR). This is not a new phenomenon. Actually, it has been researched since the mid 1950's but for some reason, I don't remember being taught it at University. Always a bit sceptical of learning something new, I initially wasn't sure how important the FRR was? What I mean by this is that, if I could see from the way my patients moved that their muscular patterns weren't correct, did I need to quantify that in order to treat it?

Well, Rob asked some brilliant questions which have stayed with me since and opened my eyes to how deep our clinical reasoning can become. 

Deciphering the driving mechanisms behind LBP

Let's backtrack a little....

  • Q: A patient presents with LBP... is it a specific or non-specific problem? A: Non-specific.
  • Q: Is the pain centrally or peripherally driven? A: peripherally.
  • Q: Do that have LBP or pelvic girdle pain? A: Low back pain
  • Q: Are their movement patterns adaptive or maladaptive? A: Maladaptive.
  • Q: Do they have a control impairment or movement impairments? A: A movement impairments - characterised by high levels of muscle guarding and co-contractions.
  • Q: What direction is most provocative? A: forward bending (flexion).
  • Q: What do you see when you bend forward?
  • Q: How can you objectively measure this? 
  • Q: How can you prove this is related to their pain?
  • Q: How do you know if the movement pattern is normal or not?
  • Q: Will modifying their movement pattern help?

This is a hypothetical case but see how the answers stopped? Well, that is a reflection of where my thinking was up to before I met Rob. I thought the puzzle was solved. When in fact Rob showed me that the questions continue and more importantly, that we are still searching for the scientific/research answers to some of them. 

What we have learnt over time is that LBP is not a homogenous group of conditions. We've learnt that some people have specific patho-anatomical or structural causes to their pain while others don't. We've learnt that sometimes our deep-stabilising muscles start to behave differently, but not in everyone. We've also realised that movement patterns can be pain drivers too. Now we are in search of the best way to determine why maladaptive movement patterns arise and if they are modifiable and what we can do about it? This comes down to the concept of modifiable movement patterns

Lumbopelvic rhythm is the coordinated movement between the lumbar spine and hip joints, connected by the pelvis, that allows us to move our trunk (Kim., 2013). Often that coordination of movement can be altered and lead to load in static positions, load through range and end range load on structures in the lumbar spine.  Unfortunately, there is no consistent movement pattern that matches back pain and everyone moves slightly differently just as the cause of pain varies between individuals. Unfortunately it can't be a 'one size fits all' approach. 

The purpose of this blog is to explore these few questions. 

What is the flexion relaxation response (FRR)?
What do you see and how can you measure it?

What strategies do we have to restore a normal FRR?

What is the flexion relaxation response (FRR)?

During flexion the erector spinae muscles act eccentrically to control flexion until the very end of range, where there is a sudden decrease in muscle activity. This is referred to as the flexion-relaxation response (FRR), and is important for achieving full range (Kim, et al., 2013; Zwambag & Brown, 2015). 

Ideally, during normal movement lumbar flexion is initiated by the lumbar spine. During the first half of available range the movement is led by the lumbar spine. Following this and towards the end of forward bending, the hips begin to contribute more to the available range. The FRR is important for allowing the full expression of lumbar flexion to occur and has been reliable found to occur in normal subjects (Neblett, et al., 2014). 

Research has shown that when the paraspinal muscles come into stretch they trigger mechanoreceptors in the joints and passive structures. This in turn triggers a stress-inhibition reflex to occur, causing the paraspinal muscles to become inhibited and the passive structures continue to provide the stability at the end of range (Kim, et al., 2013). This is described as a load-sharing mechanism between active and passive structures (Zwambag & Brown, 2015). The angle at which this phenomenon occurs is often referred to as the absolute flexion angle (Zwambag & Brown, 2015). 

Some studies exploring the FRR has found that patients with low back pain are often over-active through their lumbar erector spinae muscles, which hardly switch off, and theorise that this over-activation contributes to over-loading of the spine and altered load-sharing capability of the tissues (Kim, et al., 2016). Thus, if the FRR is a vital part of movement into flexion and studies have shown that it can be absent or altered, then it begs the questions of how we are currently measuring movement patterns in the lumbar spine during assessment?


In the clinic you might use a goniometer for range of movement, measure finger tips to floor, or how far the hands slide down the shins. Experimentally, some studies use 3D video analysis to measure range and contribution to movement of the lumbar spine, hip and pelvis, and surface EMG to understand muscle activity (Kim, et al. 2013). A meta-analysis has shown that surface EMG combined with ROM analysis can increase the sensitivity (88.8%) and specificity (81.3%) of assessment (Geisser, et al., 2005, p. 721). Essentially what this means is that we need to continue to look for ways to improve our measure in order to determine what type of movement pattern we are trying to treat. 

There are devices on the market which measure EMG activity during static and dynamic movements, but the reliability and clinical utility of these are currently being explored but researchers such as Rob. Clinically, I still rely on visual observation as my main measure of range of movement but now I look at a few more elements than previously. 

  1. How much range do they have?
  2. What is the limiting factor - pain, stiffness, end of movement? 
  3. What does their movement look like? Are they flat through their back or very rounded? Do they use both the lumbar spine and hips during range? 

Sometimes it is easy to see the problem but other times it is disguised. I remember during the masterclass Rob showing a series of videos and asking us to describe if we thought the movement was coming from the spine, or hips or both. On several occasions, what looked like limited lumbar flexion was actually too much lumbar flexion or vice versa. Essentially, the point that Rob was trying to show us is that our eyes don't always see exactly what is going on and where the movement is coming from and perhaps, devices that measure EMG activity during different ranges of movement can assist our assessment. It is important during assessment to be consistent. Which ever methods you choose, try use them in a reproducible manner. 

What strategies do we have to restore a normal FRR?

Once you have measured lumbar active range of movement and determined that the FRR is impaired, you next need to try determine what the limiting factor is. Is flexion painful and limited because the hips aren't contributing enough? In that case, what factors are impede hip flexion? Or, is the lumbar spine remaining in too much extension and why would that be the case?

Ideally, you will always take the movement pattern into consideration as a component of the entire assessment. For example, the patient might be overusing their lumbar spine but they have a hyper-mobility syndrome and their mechanoreceptors don't get activated because their joints and ligaments aren't on stretch at the end of range. Logically, continuing to move these patients into flexion might not be a great approach. Alternatively, repeating movement into flexion might also not be a great approach when a patient uses too much lumbar range because they have tightness through the posterior structures of the the hip that prevent hip flexion. 

Therefore, you might address contributing factors such as flexibility in the posterior hip structures such as calves, hamstrings, gluteals and structures in the posterior chain. You may wish to loosen any tightened structures in lumbar spine contributing to it staying in relative extension. Or, you might try retrain the lumbar flexion movement pattern. This last approach can be down in progressive ways:

When retraining flexion remember that the main focus is to encourage relaxation at the end of range. If the patient is guarded or experiencing pain, then the exercise position is not appropriate. I've always begun with child's pose as it addresses all the elements we need i.e hip flexion, lumbar flexion and the floor supports the patient allowing them to focus on their breathing. Once relaxation is achieved in this position, the seated forward fold is the next step and patient's have their upper body supported as they rest on their thighs. Again, focussing on breathing and letting go. The final progression is in the posture they originally found provocative and this would be down in the later stages of rehab. 

What if the movement is painful and you can't use these techniques?

If these movements are too painful or uncomfortable for your client, and you still believe they need more relaxation through the lumbar erector spinae, then I have found lumbar rotation to be a great alternative. What we know about the back muscles is that they work bilaterally to create extension and unilaterally to create rotation. So as we rotate from side to side, one side is activating and the other relaxing. It's a good starting point to gain relaxation of muscles, encouraging control of movement, teach breathing control in a painfree position. 

Hopefully this blog has given you some new tools in the treatment of LBP. It is nothing new or fancy but a strong reminder to take time to perform a thorough and careful assessment of the main problem and the movement patterns around that.  

For me, it is a reinforcement that we constantly need to be linking assessment and treatment and proving that strategies are helpful. While we continue to search for data and answers, we just need to focus on applying our clinical reasoning to choose the best treatment for the best person. I definitely think this is a "watch this space" topic and that in the near future we will have developed and researched better ways to objectively measure lumbar movement, analyse the movement patterns we find, and strategies for normalising the flexion relaxation response. 

Sian :)


Geisser, M. E., Ranavaya, M., Haig, A. J., Roth, R. S., Zucker, R., Ambroz, C., & Caruso, M. (2005). A meta-analytic review of surface electromyography among persons with low back pain and normal, healthy controls. The journal of pain, 6(11), 711-726.

Hu, B., Shan, X., Zhou, J., & Ning, X. (2014). The effects of stance width and foot posture on lumbar muscle flexion-relaxation phenomenon. Clinical Biomechanics, 29(3), 311-316.

Kim, M. H., Yi, C. H., Kwon, O. Y., Cho, S. H., Cynn, H. S., Kim, Y. H., ... & Jung, D. H. (2013). Comparison of lumbopelvic rhythm and flexion-relaxation response between 2 different low back pain subtypes. Spine, 38(15), 1260-1267.

Laird, R. A., Kent, P., & Keating, J. L. (2012). Modifying patterns of movement in people with low back pain-does it help? A systematic review. BMC musculoskeletal disorders, 13(1), 1.

Neblett, R., Mayer, T. G., Brede, E., & Gatchel, R. J. (2014). The effect of prior lumbar surgeries on the flexion relaxation phenomenon and its responsiveness to rehabilitative treatment. The Spine Journal, 14(6), 892-902.

Zwambag, D. P., & Brown, S. H. (2015). Factors to consider in identifying critical points in lumbar spine flexion relaxation. Journal of Electromyography and Kinesiology, 25(6), 914-918.