Sitting and Spine
By Dr. Jerome Fryer, Chiropractor
For decades, we’ve been told to “sit up straight.”
It’s common advice, and modern biomechanical research continues to support it. But an interesting question remains:
What if posture is only half the equation?
A recent finite element study published in Bioengineering examined how different sitting positions affect stresses within the lumbar spine during movement. Rather than measuring living subjects directly, the researchers created an anatomically detailed computer model of the lumbar spine and simulated common movements while standing, sitting upright, slumped sitting, and sitting on the floor.
Their findings reinforce an important principle that clinicians have suspected for years.
Posture Matters More Than Many People Realize
The study found that an upright sitting posture that preserved lumbar lordosis produced stress patterns remarkably similar to standing.
In contrast, both slumped sitting and sitting on the floor substantially increased stress within the:
- annulus fibrosus
- nucleus pulposus
- vertebral cortical bone
This occurred not only during quiet sitting but also during flexion, side bending, and rotation.
The message is straightforward:
Loss of lumbar lordosis changes how forces are distributed through the spine.
That increased mechanical loading may contribute over time to disc degeneration and other spinal disorders.
But There Is Another Variable
The study focused on how posture changes spinal loading.
It did not investigate another important question:
Can we reduce the load itself?
These are fundamentally different biomechanical concepts.
One changes spinal alignment.
The other changes the amount of compressive force travelling through the spine.
Imagine carrying a heavy backpack.
Improving your posture helps distribute the load more efficiently.
Taking the backpack off reduces the load altogether.
The lumbar spine behaves in much the same way.
Offloading Through the Upper Extremities
One fascinating strategy that deserves greater investigation is using the arms to temporarily support part of the body’s weight.
Instead of allowing all upper body forces to pass directly through the lumbar discs, some of those forces can be redirected through the shoulders and upper extremities.
Mechanically, this decreases the compressive force acting on the lumbar motion segments.
This concept is surprisingly underexplored in the scientific literature.
Our Earlier Research Demonstrated This Principle
In 2010, our pilot study investigated what happened after participants sat for 15 minutes and then performed a simple seated unloading exercise while supporting themselves through their upper extremities.
Using upright MRI together with seated stadiometry, we observed measurable changes immediately following unloading.
Compared with the compressed sitting posture, participants demonstrated:
- increased lumbar disc cross-sectional area
- restoration of lumbar lordosis
- increased lumbar spinal height
- recovery of seated body height
These changes occurred within minutes following the unloading exercise.
Although the study was small and designed primarily as a feasibility investigation, it demonstrated that upright MRI could detect measurable morphological changes associated with temporary spinal unloading.
The findings suggested that unloading may produce rapid biomechanical changes worthy of much larger clinical trials.
Posture Plus Reduced Compression
What makes the new finite element paper particularly interesting is that it confirms something our earlier work also suggested.
Maintaining lumbar lordosis reduces stress.
But restoring lordosis may not be the entire story.
Reducing compressive force may provide an additional biomechanical advantage.
These two strategies may be complementary rather than competing.
Good posture optimizes force distribution.
Offloading may reduce the magnitude of those forces altogether.
Future research combining these approaches could provide important insights into preventing mechanical overload during prolonged sitting.
Why This Matters
Many people spend eight or more hours each day sitting.
Simply telling someone to “sit up straight” may not be sufficient, particularly during prolonged desk work or recovery from spinal injury.
Perhaps we should also ask:
- Can we periodically reduce spinal compression?
- Can brief unloading exercises interrupt prolonged disc loading?
- Could upper-extremity-supported offloading become part of spinal health strategies in the workplace?
These remain important research questions.
My Clinical Perspective
One aspect of biomechanics that continues to interest me is that the spine is not simply a rigid stack of bones.
It is a living mechanical structure whose tissues continuously respond to loading and unloading.
Understanding not only where forces are applied, but also how much force is transmitted through the spine, may help explain why some interventions succeed while others have only modest effects.
The recent finite element study strengthens the evidence that posture matters.
The next step may be investigating how posture and active spinal offloading work together to influence disc mechanics, spinal health, and ultimately patient outcomes.
References
Cho M, Han JS, Kang S, et al. Biomechanical Effects of Different Sitting Postures and Physiologic Movements on the Lumbar Spine: A Finite Element Study. Bioengineering. 2023;10(9):1051.
Fryer JC, Quon JA, Smith FW. Magnetic resonance imaging and stadiometric assessment of the lumbar discs after sitting and chair-care decompression exercise: a pilot study. The Spine Journal. 2010;10(4):297-305. doi:10.1016/j.spinee.2010.01.009.