It turns out that cautions like these are based on a “lever system” model of the body which is limiting in its scope and is quickly becoming outdated. This model views the body, and especially the spine, as an inherently fragile structure that is quite vulnerable to injury when it experiences compressive forces. But a more current and accurate model of the body is that it is a naturally resilient biotensegrity structure whose tissues are supported three-dimensionally and have the ability to adapt to the demands placed upon them, thereby becoming stronger and better able to withstand load in the future.
Forces affect biotensegrity structures like the human body (new model) differently than they affect lever systems like machines (old model). Of course if the spine were to experience a high load while in a position of flexion (like in heavy weightlifting, for example), it could certainly be injured. But basic unloaded and low-loaded spinal flexion is a safe and natural movement for healthy spines.
When we pathologize a particular movement and tell people that it is inherently damaging, we create a significant amount of fear around that movement. When we have fearful beliefs about a movement, our brain is more likely to output pain for us when we do that movement (also known as a nocebo). This pain very likely has nothing to do with any actual tissue damage being caused by the movement, and instead has everything to do with beliefs and fear surrounding the movement. This will result in our participating in the movement less and less (sometimes called fear avoidance), which can cause us to lose mobility and range of motion in that direction of movement. (For more on this fascinating topic, you might be interested in viewing a workshop I recently taught on the anatomy of healthy spinal movement!)
Beliefs about pelvis-tucking and lumbar flexion have moved from one end of the spectrum to the other in recent times. A current trend in the yoga world is to not teach or practice this movement at all because it is inherently harmful to our bodies. I am hopeful that our yoga community will settle on a more nuanced, less fear-based view of this issue in the near future. Our pelvis and spine and their adaptive, resilient tissues were designed to move in many different ways, and to keep these areas healthy and functioning well, we should move them in all of these ways on a regular basis. And when it comes to the specific yoga asanas that we teach or practice, we should let our anatomical intention for each pose - and not a one-size-fits-all rule - determine the pelvic positioning we teach.
FURTHER READING & EXPLORATION
If this is the first time you’ve heard this progressive message about lumbar flexion, here are a few suggestions for further reading and exploration on the topic:
-Jules Mitchell, M.S. - Watch her online class called Limber Lumbar (great name!) on the websites Udaya or Yoga Anytime, or even better, take her excellent Science of Stretching lecture series!
-Literature review research article: “To Crunch or Not to Crunch: An Evidence-Based Examination of Spinal Flexion Exercises, Their Potential Risks, and Their Applicability to Program Design” by Bret Contreras & Brad Schoenfeld
-Spinal Flexion Is Important for Low Back Health and Strength by Dean Somerset
Related Post: A Biomechanics-Informed Response to Yoga Journal: We Do Not Need To Tuck Our Tail In Every Yoga Pose
Related Post: Core Strength Fiction & Facts
Related Online Workshop: Anatomy of the Spine for Increased Core Connection