Last week, we talked about the biological properties of tissues, the concepts of tolerance, and some factors that increase injury risk. This week, we’ll direct a more specific focus toward how the spine itself is loaded and cover a few injury types that you’ve likely heard of.

How the Spine is Loaded

Gravity pulls everything on the surface of our planet towards the Earth’s core. Because of this, even when sitting or standing, with no external load, our spines experience compressive forces along their longitudinal axes. The spine itself is a semi-rigid structure and requires muscle attachments for stability and movement. Any muscle that connects to, or across, vertebrae adds compressive forces to the spinal column.

Compression itself isn’t inherently bad. Our spines actually require compressive forces to exchange certain proteins into and out of discs [1]. And mechanical loading through compression is required for cellular processes of tissue homeostasis [2]. Think of loading like Goldilocks and the porridge she gets from the three bears; she likes it not too hot and not too cold, but just the right temperature. It’s the same for the compression of our spines.

In fact, a great example of too little loading comes in the form of astronauts. There’s an increase in cervical and lumbar disc herniations when they come back to Earth [3]. Researchers proposed that weightlessness may have caused:

• prolonged disc swelling,
• atrophy and weakness of muscles surrounding the spine, and
• flattening of lumbar lordosis (normal curvature of the lumbar region)

[4].

Our spines are carefully tuned to the conditions on Earth and have adapted to our diurnal loading cycles (increased loading during the day, and decreased loading as we sleep). Anyway, you get it — too little loading is bad…and so is too much.

Before I get into the painful examples of what can fracture, herniate, and otherwise, I want to pause and make a point.

“Your spine is not fragile when you support it” — Mitch Whittal, 2026.

Spines can tolerate incredible forces when lifts are performed in proper postures. The hard part is training our muscular systems to maintain proper postures as loads get heavy. Don’t get me wrong, there are certainly movements that I wouldn’t recommend from a spine biomechanics perspective, and we’ll get into that, but the point is simple — compressive forces alone are likely not the problem leading to your injured back and back pain. So how does your spine do it?

Well, it all starts with the jelly-filled onions between your vertebrae — our intervertebral discs. Our discs act as shock absorbers, where compression of the jelly-like center, the nucleus, causes radial (horizontal) expansion. Radial expansion is resisted by the annulus fibrosus, the proverbial layers of the onion. In a neutral position, the nucleus pushes out on the annulus, and the disc absorbs the compressive force.

Injuries

With injuries, we tend to see complex loading scenarios that combine compression with repetitive flexion and extension (rounding forward and then extending back past neutral). Other combinations involving twisting, surprise/rapid loading, and other unique loading combinations also produce injuries, but we’ll just focus on one for the intervertebral disc and one for our vertebrae.

As our spines move into flexion, the jelly gets pushed to the back inner layers of the onion. At the same time, the posterior onion is being pulled into tension by its attachments to the vertebrae through endplates. This causes what is called a ‘stress concentration’ on the inner layers of the posterior annulus.

Over time, with enough repetitive cycles of flexion and extension (especially with additional compressive loads), the nucleus claws and fights its way out of the annulus one layer at a time [5]. This can happen rapidly with large compressive loads while in flexion as well, often breaking off a piece of the endplate/vertebra where the disc connects to the vertebral body [6].

The deviations from a neutral posture, or natural curvature, of the spine are what cause the stress concentrations on small areas, leading to forces that exceed the tissue strength threshold and a resulting injury. In a neutral posture, the internal forces from the compressed nucleus are more evenly distributed around the inside of the disc. This prevents the forces from exceeding the injury threshold.

Vertebral Fractures

While disc herniations get a lot of attention, the vertebrae themselves can also fracture. Fractures to the vertebral body tend to happen in neutral or flexed postures when rapid compressive loading is applied. So, in neutral postures, the disc typically doesn't fail, but the vertebral body might. This is because the internal stresses of the nucleus are more evenly distributed in neutral postures, so the vertebral bodies and endplates become the new weakest link. During rapid pressurization of the nucleus, there was consistent failure of the endplates in young hydrated pig spines (often used in tissue research) [7]. This ‘rapid pressurization’ of the nucleus is experienced during explosive athletic movements.

Then, later in life, as intervertebral discs lose hydration naturally, there is an increased risk of vertebral body fracture. As discs lose hydration, they lose some of their previous ‘shock absorber’ capability. When the spine is subjected to a large amount of compression in a flexed position, this disc is not able to dissipate force as effectively, and it is transferred to the anterior vertebral body. Anterior vertebral body fractures, sometimes called ‘wedge fractures’ are often the result of traumatic events like falls, heavy lifting, or car accidents in the elderly. Osteoporosis often plays a role in these fractures as well. Gradual decreases in bone density leave vertebrae vulnerable to injury.

Wrapping it all up

What can we take away from this? There’s a clear answer: do your best to remain in neutral spine positions and brace your core when lifting. Here’s how to brace your core in a couple of easy steps:

1. Breathe in and expand your belly.

2. After expanding, tense your stomach as if someone is about to punch you there. Keep breathing while holding the brace; it should feel supportive, not like you are holding your breath.

3. Use this light brace before and during movements that load your back (bending, lifting, getting up, carrying something).

For those with sensitive and sore backs, remaining in stable, neutral postures will help protect you from further damage and pain. And frankly, this is something that should be taught to everyone so that we don’t all end up reading this newsletter trying to learn where it all went wrong.

What else? It should be apparent by now that it’s incredibly important to surround your spine with strong muscles to protect your posture. Resistance training and corrective exercises build strong, resilient backs that can hold the line when life demands a lot of our backs — and they help prevent the loss of bone mass seen in osteoporosis! If you’d like to learn how to make your back more resilient, you can head to my website linked below to perform an assessment and get your personalized program.

Thank you again for tuning in this week. I’m working on some exciting upgrades to our assessments and associated products, and I can’t wait to share them with you in the coming weeks.

As always, have a great weekend,

Mitch

References

1. Urban et al., 2004: https://journals.lww.com/spinejournal/abstract/2004/12010/nutrition_of_the_intervertebral_disc.14.aspx
2. Chan et al., 2011: https://pubmed.ncbi.nlm.nih.gov/21541667/
3. Belavy et al., 2016: https://pubmed.ncbi.nlm.nih.gov/25893331/
4. Bailey et al., 2017: https://pubmed.ncbi.nlm.nih.gov/28962911/
5. Tampier et al., 2007: https://pubmed.ncbi.nlm.nih.gov/18246010/
6. Wade et al., 2015: https://journals.lww.com/spinejournal/abstract/2015/06150/_surprise__loading_in_flexion_increases_the_risk.6.aspx
7. Brown et al., 2008: https://pubmed.ncbi.nlm.nih.gov/17706227/