Is Flexion Really “Bad” for the Spine?
In some schools of thought and training, flexion is not good for the spine – ever. This would include spines with osteopenia or osteoporosis (which we will call bone density loss from here on) – and healthy spines with no pathology whatsoever.
The rationale given is that the spine is not built – or meant to – articulate, but instead to be stable and that one should NEVER flex the spine because it is dangerous. These opinions further state that segmental articulation, even cat-cow, is not recommended.
The spine’s primary purpose is protection of the spinal cord and force or load transfer from the extremities to the trunk and vice versa.
How Much Flexion?
There are differing opinions about how much flexion – if any – are actually safe for the spine, for people who have bone density loss. Why would we not be able to agree on how much flexion is safe – and how much is too much? We simply do not know the answer. We do not have any studies in which living humans are in double-blind tests in which the spine is loaded until it collapses. It would be inhumane to do so.
However, there are two studies we can refer to that used in vitro specimens; Stuart McGill has worked with pig spines for years, loading them until they broke – testing different loads on the spine.
His research shows that repeated loading in one direction will result, over time, in disc herniations: “ There are only so many bends in your spine until the discs eventually herniate.” (1)
A 30-year study published in 2024 used human spines to test ROM to find norms for flexion, extension and rotation in the human spine. (2)
Is Flexion Dangerous?
Flexion loads the anterior aspect of the vertebral bodies, and intervertebral discs. The vertebral bodies, composed of cortical and trabecular bone, become less structurally strong in a person with bone density loss. If the discs are degenerated (degenerative disc disease or DDD) then they are also less resilient. To load the degenerated spine unevenly for extended periods of time – or to purposefully load the spine in flexion – this is a potential risk.
But what about the healthy spine with no contraindications? Why would flexion be considered “dangerous” for this spine? A rationale is that the shoulders and hips are built to move in greater ranges of motion (ROM) than the spine, due to their ball-and-socket joints. The spine, then, is meant to be stable while the appendicular skeleton – the hips and shoulders – are meant to provide the greater ROM.
This thinking works – somewhat. It is true that ball-and-socket joints have more ROM in all planes of motion than the spinal joints. Thinking about my practice, though, for years I have worked with people whose shoulders and hips suffered degenerative conditions that in many cases were a direct result of lack of integration of shoulder and/or hip movement with trunk movement – and the basis of trunk movement is spinal movement. For people who have partial or total spinal fusion, maintaining or improving the mobility of the hips and shoulders is paramount. Our human bodies are meant to work so that the forces and loads of movement are shared amongst multiple related structures, so if one area has less potential for movement, that ROM is transferred to the next mobile joint or area.
The Spine Is Meant To Move
Here’s a thought: if the spine isn’t meant to move, why is it made of 24 movable joints instead of one long bone? The joints of the spine are cartilaginous, and between these are the fibrocartilaginous intervertebral discs, and the synovial facet joints all allow for segmental movement.
Last, there is no direct blood supply to the intervertebral discs. They are avascular and depend on the pumping action created by movement to receive nutrition and lubrication, and to eliminate waste products. (3)
So if the spine is meant to move, in fact needs to move, where does the problem lie? In my opinion after looking at multiple studies, combined with 25 years of clinical experience as a spinal pathologist and pathokinesiologist, I have distilled these questions into 3 main areas to consider:
Three Considerations
- Relationship to gravity: depending on body position, the spine has varying degrees of pressure on the spine. (4) There are multiple studies that report variances in how much pressure, but all the studies agree that there is more pressure on a spine and its intervertebral discs when the person is sitting or standing in flexion, less when they are standing upright, still less when they are lying down. Therefore, movements that could be harmful or risky in a more loaded position may become less risky in a less-loaded position – and may even become beneficial. If a person has -2.5 or more bone density loss on their DEXA, and they have previous fractures, we consider them fragile. This is the person whom we will coach to avoid all flexion, teach to hinge from the hips, and log-roll to transition to and from lying down.
- Long-term uneven vertebral loading: there are norms established for what is considered “neutral” curvatures in the spine. These norms are ranges because we are all individuals with structural differences. Instead of thinking about numbers, let’s think about the vertebrae stacked atop each other in a spinal column. Optimal loading will have the intervertebral discs and vertebrae stacked fairly evenly front-to-back and side-to-side. If we look at structural differences such as hyperkyphosis, we can assume that the anterior aspect of the vertebrae and the intervertebral discs will have more sustained pressure. Over time, this creates more load on the vertebral bodies and the discs. Our bodies adapt to these types of sustained pressure with changes such as disc dehydration or herniation (from the sustained pressure on the nucleus pulposus toward the back of the body), and hypermineralization like arthritis of the vertebral bodies – which makes both the vertebrae and the discs less resilient. This is the person for whom we need an extension-biased plan, as why would we load the same posture, further exacerbating already compromised structures? For this reason I discourage upper-body lifts (a.k.a. crunches) for people with hyper-kyphosis.
- Repetitive movement patterns: these are both exercise-dependent and activities of daily living (ADLs). We can see how a person who has a one-sided rotational job or sport will eventually create a work-or-sport adaptation strengthening rotation in the habitual direction. We can also see how a person who is sitting at their desk all day is in a position in which the spine is under constant load in a flexion-bias and the resulting lack of movement reduces the pumping action which our spines depend upon for circulation and lubrication. This is what I call a position of dehydration: the pressure removes fluid and inhibits uptake of fluids, similar to squeezing a sponge but never releasing it. Over time, loss of disc height occurs, bringing the vertebrae closer together, and ROM is lost. A person who is already unevenly loaded during most of their life needs cross-training for their spine; bias the program in the other direction, emphasizing less load and more opportunities for uptake of fluids to improve cellular nutrition in the spinal structures.
Program Design Tips
- Practice consistent decompression: the Kitchen Sink Hang, Hanging with Feet on the Floor, using a K spine decompression wedge (4) are all ways to reduce the load of gravity and provide an environment for improved circulation and spinal movement.
- Think spinal “cross-training:” if the person is in a position of sustained flexion, extension, or rotation, gently introduce the non-habitual directions in the form of exercises, always after decompression.
This might look like an extension-biased program for someone who has hyper-kyphosis, and a flexion-biased program for a person with a flatter spine, such as a dancer. This may look like a 2:1 ratio of rotational exercises, favoring the non-habitual side for a person who has a rotational imbalance.
People who have scoliosis are a different case, and need more specialized intervention, so in these cases, decompression followed by direct back strengthening (a.k.a. “postural” strengthening) is a good place to start. It is best not to try to “correct” the rotations of a person with scoliosis until an understanding of scoliosis-specific assessment and exercise is in place.
- Choose movements based on their relationship to gravity: While a standing rolldown or an abdominal crunch creates more pressure on the spine, and seated flexion even more, similar movement such as supine pelvic tilts or quadruped flexion-extension (a.k.a. “cat-cow”) in small non-end-range ROM can be a wonderful way to introduce spinal movement, promote lubrication and circulation within spinal structures, and teach the person to listen to their body, ascertain their safe ROM, and feel the benefits of spinal movement.
Personal Autonomy
Lastly, we need to consider the role of autonomy, or agency when working with people. It is ultimately each person’s own responsibility to manage their own body. We can guide, educate, suggest, increase awareness, and do our best when working with people.
Ultimately, our purpose is to help the people we work with make better decisions about movement when they are not with us, living their lives. To bring awareness of sustained postures and repetitive movement patterns that a person can begin to alter in their day-to-day life is a great service, and empowers each person to create change that provides benefits including pain reduction, more ease of movement, improved ROM, and perhaps even slowing down or reversing degenerative changes due to poor movement mechanics or uneven loading.
I believe what we don’t need is to instill fear of movement, creating stiffness or bracing, which increases compressive load on the spine and joints, reduces the potential for circulation and lubrication at the spinal level and can be a factor in creating pain. Our bodies are amazingly resilient and adaptable when we give them what they need; good movement!
Want to dive deeper?
Join Gwen in Foundations or the Safe Movement For All Spines Mentorship.
References
- Range of Motion and Neutral Zone of All Human Spinal Motion Segments: A Data Collection of 30 Years of In Vitro Experiments Performed Under Standardized Testing Conditions
– Hans-Joachim Wilke1 | Annette Kienle2 | Karin Werner1 | Christian Liebsch1 1Institute of Orthopaedic Research and Biomechanics, Trauma Research Centre Ulm, Ulm University Medical Centre, Ulm, Germany | 2SpineServ GmbH & Co. KG, Ulm, Germany
- Grunhagen T, Wilde G, Soukane DM, Shirazi-Adl SA, Urban JP. Nutrient supply and intervertebral disc metabolism
– J Bone Joint Surg Am. 2006 Apr;88 Suppl 2:30-5. doi: 10.2106/JBJS.E.01290. PMID: 16595440.
- Safe Movement for All Spines: A Guide to Spinal Anatomy and How to Work with 21 Spine and Hip Conditions
– Gwen Miller, 2023