Dr. Stuart McGill has been heavily influential in my education and professional development. He is a professor emeritus, University of Waterloo, biomechanist and researcher. I've collected countless bits of wisdom from the man himself, and those who have worked with, or studied under him. The following post is not exactly my original content. The concepts are a collection from these sources put into my own words. This post is a way to consolidate all of these ideas, and also present it in a way that could be helpful to the reader here as well as the people I work with.
The spine is a flexible rod. It is held up by a system of guy-wires consisting of muscle and other connective tissues. This system is crucial. If you were to take the spine outside of the body, a mere 20 lbs added would cause it to buckle and bend. In order to bear load the system of guy-wires needs the ability to stiffen. This stiffening happens in a beautiful, coordinated effort by the surrounding tissues.
It is proven that the majority of back injuries are cumulative in nature. With this in mind it would make logical sense that we'd wish to limit excessive spinal motion under load. We don't want to accumulate trauma to the spine. As an example, if a person was bending over to pick up a potted plant there would be some pressure on the spinal discs. If this person generated power from the hips pressure would be minimized. However, if this person bent forward at the spine there would be tremendous posterior stresses. Over time the nucleus of the disc will travel through the layers of the disc annulus as they separate under the repeated stresses. This is what causes a disc bulge.
This is one example of how poor movement mechanics can accumulate stress over time. When we generate power from the spine for too long it will fail. The incident where the injury is felt is usually the straw that broke the camel's back. It's often an innocuous bending over to pick something up, or forgetting to keep good form when setting the weight back down in the gym.
The athletic greats use their hips, and shoulders for power production, but their core for stiffness and power transmission. Generally when you generate power from your spine it will begin to break (see above). That's why good body mechanics rely on the big movers like the hips and shoulders. The spine stiffens using that nifty guy-wire system. The spine's inability to stiffen can cause injury. Interestingly, the ability to stiffen can allow us to transmit power to a greater degree in the bigger movers. "Distal movement requires proximal stiffness."
The greats like Pavel Tsatsouline describe strength as a skill. Something to practice. When practicing strength in the gym you should be ingraining movement patterns of effective spinal stiffening especially when handling load. When the core fails to meet the stability demands placed on the body during a certain task, the spine will be overloaded with forces that increase risk of injury, AND if you're participating in athletics, performance will suffer.
Research has found that isometric exercises enhance muscular endurance. They are far superior when compared to dynamic strengthening exercises in enhancing spinal stiffness and stability. This makes them ideal for rehabilitation AND the enhancement of athletic performance.
An isometric exercise is when a group of muscles are activated / contracted, but there is no change in the joints they cross. For example, during a side-plank the lateral oblique and quadratus lumorum muscles are very active, but the spine and hips remain still.
The core functions to limit excessive motion rather than creating it. This begs the question, why would we train in excessive spinal movement? Especially when evidence suggests injury comes from cumulative exposure. The gym should be where we practice for life. Picking up a potted plant might look something like a deadlift. When we practice the deadlift emphasis is placed on proper bracing (spinal stiffness). You can see the direct translation from gym to life.
Stiffness and stability is incredibly important for the core. We can train stability with isometric exercises, but there are other considerations. Hip, thoracic, and shoulder mobility. In a movement like the squat, lack of hip mobility may cause excess lumbar movement which is no bueno if you've got a barbell loaded with weight.
You do not need to avoid all spinal movement. Variety of movement is important. However, when adding load and lots of repetition we should default to our correct movement patterns.
We should be aware, even with all this information to consider, that the human body is highly resilient and adaptable. In fact, even when there is a bulge, or protrusion it is often not even felt. In a study of 98 asymptomatic individuals (no pain or symptoms), 52 percent of the subjects had a bulge at at least one level, 27 percent had a protrusion, and 1 percent even had an extrusion. Thirty-eight percent had an abnormality of more than one intervertebral disk. The prevalence of bulges, but not of protrusions, increased with age. Similar studies have been done around other joints of the body. Again, these were bulges with no pain. We're finding large percentages of the population have these "abnormalities" without issue. It seems as though we should look at them more like "normalities."
All this to say, we shouldn't be afraid of movement, or hurting our backs. We can take proper precautions, and even "prehab" with isometrics. This should get our spine stiff, stable, and ready to meet the demands of life.