Elastic properties of spinal discs (part 1 of 2)

Grasping an understanding of the physics and behavior of an elastic material is key to understanding and diagnosing spinal disc pathologies. Spinal discs have very similar properties to a car tire which behaves much like many elastic systems under various forces against it.

Spinal discs are made of fibrous cartilage filled with fluid to provide elasticity, much like a tire is filled with air. Here are the 4 kinds of forces a disc is subject to with varying degrees depending on function and activity.

1. Gravitational forces

   Gravity is a vertical force that produces impact on the disc. It can be abrupt or cumulative, and ultimately compresses the fluid inside of them which can bulge or herniate under pressure.

2. Momentum

   Horizontal forces produces sheering or friction against the disc material, and is most pronounced when your body is moving in a particular direction and stops abruptly. This exaggerates the force against the disc material and can weaken the fibers over time if the forces exceed the material strength of the disc

3. Rotation

   Twisting motions against an elastic material has physical limits. Spinal discs are most vulnerable to rotational forces, especially when coupled with momentum and gravity.

4. Decompression

   These forces include pulling or traction against the disc, and is evident when your body is hanging freely (like on a pull-up bar). Sleeping positions may not be enough to decompress because muscle tension can be present to act in a compressive direction even under the best sleep circumstances, but it can help reduce the effect of gravity and momentum, but not always rotation.

Functional and Dysfunctional Forces

The tires of a car provide excellent cushion and traction for a vehicle that is intended to travel, carry loads, and maybe even go offroading. The health of the tire depends on many factors, including the integrity of the rubbery material holding in the air, the amount of exposure to temperature, the cumulative load it carries on a regular basis, the kind of tasks it performs, and even the environment in which it spends it time in.

Our spinal discs are exposed when there is more load to carry, like during exercise or when we are heavier than we ought to be. It is exposed when performing abrupt horizontal forces like momentum during running or sprinting and changing direction. Twisting motions during the day may be harmless but can be a trigger source for a disc that is vulnerable or experiencing injuries.

Day to day activities like work, self care, sitting and standing is like a car that travels on the same road daily, with predictable obstacles along the way, no real surprises and should not be a source of hardship. But if that car gets into a fender-bender, is not maintained, low on fuel, exposed to the elements, etc., that car becomes a bit more of a challenge to drive even on the routine days.

Exercise is like taking your car off it's routine path and onto the the gravel road, maybe a few potholes along the way, and perhaps an abrupt stop to avoid a collision. Fortunately, your body is designed for resilience and can adapt to the hardships you experience, and become more robust in the future unlike your car is when exposed to hardship. But the stress can also become burdensome on the body over time and repetition if not maintained properly like with hydration, good fuel sources, sleeping, stretching, etc. Analogies will fail at some point, but understand that your body is not replaceable though resilient. Cars are absolutely expendable, and you are not!

Injuries, whether abrupt or cumulative is like your car getting out of sorts from an accident or used outside it's intended material strength. It causes the system to perform under stress, and can rapidly perform with collateral strain on other body areas.

Energy drinks, anabolic steroids, and performance enhancing drugs is like upgrading the engine without upgrading the suspension or the tires. That engine can likely perform to a greater capacity while wearing down other mechanical systems connected to the engine. A "high pain tolerance" is also like avoiding the check engine lights, often an avoidance behavior to pain and ignoring symptoms when they become apparent.

In summary, consider treating your body better than your car, and understand that the physics that puts a strain on your car's tires are the same that your spinal discs are exposed to with daily activities and exercises. Even though our bodies are beautifully designed for adaptation and resilience, it is not replaceable.

Part 2 of this article addresses the "Do's and Don'ts" when experiencing a suspected disc problem.