Okay, so I'm standing here with Dr. Stuart McGill, who's an expert in the back, back strengthening and relief of back pain. And he's going to tell us about the structure of the back in terms of where it derives its stability from, where pain can arise, and various routes by which to relieve that pain.

So why don't you explain to us what you're holding here. It looks like an anatomical model of a piece of the spine, spinal cord and pelvis. That's just about it, professor. If I was to align this on yourself, that's where it sits. So there's your pelvic ring. There's joints called the sacroiliac joints from behind, where when a person does a split lunge, for example, one side mutates forward, the other side mutates back, and you can see the micro movements that occur in the sacroiliac region, which may be healthy, or they may cause pain.

So those are fairly small movements. So they look like they're on the order of millimeters. Is that right? About a half a millimeter. Okay, so tiny movements. They're micro movements that, as I said, could cause symptoms or they indicate good health. This creates a platform for the lumbar spine.

So as it's orientated this way, if you were to pick something up, the force is supported down this middle of your body through the spine. So it needs a platform to be supported by. So you can imagine, I'll just place it on me, if I was going to stand on one leg, the force is driven down the center of my torso, but then it has to shear across to the support leg.

So the tendency of the spine is to bend like that. So now you see the importance of the lateral muscles on this side to hold the pelvic platform up and then the hip muscles on this side to start, you see my hip is trying to collapse because of gravity.

So there's a lot of moving parts in how all of this works. So as far as the spine goes itself, you know, the hips are ball and socket joints, but the joints of the spine are actually what we would call an adaptable biologic fabric. So just as my shirt has fibers, these have fibers of collagen layer upon layer, which allow movement to occur, but they also apply or provide stiffness so that the spine is inherently stable for very small loads because it has discs.

So we have the vertebral segments and then the discs in between them. And then what people see here are the nerve roots emanating from the spinal cord. Right. The spinal cord starts in the base of your skull and goes down the middle of the spine through what's called the magnum foramen, the big hole down the middle.

And at each level where there's a disc, there's a pair of nerve roots that come out laterally to serve different parts of your body. So if this nerve was compromised here, that's the fourth root on the left hand side. This goes around behind your hip joint, down your hamstring, down your calf and serves the small four toes.

So if you had irritation by bending your spine a certain way and said, well, my little toes just went numb, we would know with some precision that that's the culprit that with that precision, that nerve right there. What are some of the sources of impingement on that nerve? I could imagine the disc bulging at this location is one potential source.

I could imagine a shearing motion that would put it in contact with some of the bony elements in here. What are some other sources of impingement on the nerve? Well, exactly those two. Let me demonstrate. We're just going to do a do-si-do there with the two models. So this is a more detailed anatomical model of just one segment.

You'll notice that the spinal cord traverses up and down. So as you look down, it migrates the cord cranially. So it's pulling the spinal cord up and because it actually laces through these bony elements, the spinal cord is literally sliding up. It is. And if you were to kick forward with one leg through the hip with a straight knee, it would do the opposite.

It would pull the cord that way. But now look at the migration and the mechanics of the nerve roots. This is sliding up and down about two centimeters or for my American colleagues just over, well, getting close to an inch. So it's quite a distance, quite a translation. You can imagine now if something was rubbing that nerve root, it would irritate it with the motion.

So your question was, what are the candidates? Well, when a person is younger and if they get a disc bulge, we're just going to show a disc bulge here, inside the disc is a nucleus which is gel. It's a very thick gel. And when you squeeze the spine or I bend and pick up an object, we put compressive load onto the disc.

And if we're stacked nice and tall, you'll see the disc sees the compression as you can imagine it would in a very sort of a shock-absorbing manner. But now I'm going to bend the spine forward and squeeze. Do you see there was a delamination or a little bit of a damage and delamination of the fibers that we described earlier, they separate as the person bends forward and then the squeezing pressure creates a hydraulic effort through the delamination and you see the disc bulge just starting to occur with the nuclear gel.

And then as the person keeps moving in excess, now if you just move, we did a study on belly dancers who have tremendous gyrations in their spine, that didn't create delaminating stresses because there was no large compressive load. So motion for the spine without load is not particularly a bad thing.

But when you add compressive load, now you've pressurized the nucleus and it's pushing from behind those fibers. So now you're bulging them out a little bit. Now you can start to see how they'll separate. And if my thumb is the gel, it's seeking the crack to come through. And then that creates the disc bulge, which is a combination of motion, usually bending forward with compression.

And on a previous episode that I did about back strengthening, I mistakenly said that the spinal cord threads through a compartment in the disc. It does not. We corrected that. I should say in the show note caption, the spinal cord is posterior to the disc, correct? - Correct. - And does not course through it, but is just adjacent to it.

And the disc is however, in a position to impinge on these nerve roots if it gets extruded. And in some cases to push the nerve root against some of the bony elements causing what we call pain, right? But the pain doesn't necessarily occur at the level of the root.

It can occur at the level of innervation or further down the neural pathway. - The pain can go wherever the nerve root goes, exactly correct. So now if we start to move the nerve, the central spinal cord or at this level, it's called the cauda equina, it separates into separate roots.

But nonetheless, do you see how that root now moves as a function of your hip motion and your neck motion? So now you're frictioning the nerve past the mechanical offense. So it creates varying types of local pain and radiating pain as well. - So if there is a disc bulge and it's impinging or somehow otherwise causing pain by compressing one of these roots, irritating one of those roots as it were, what can be done to return some of that bulge back into its proper location?

- Avoid bending the spine forward, which is the primary driver of causing that disc bulge to grow. Now, not of every disc bulge. It tends to work better in younger people. So I'm just going to slide my hands down my thighs, but notice I'm flexing at the hip. I'm not flexing through the spine.

If you can flex at the hip, and here might be a therapy, if I just grab my knees hard and then I shape the curvature of my spine, then I push my toes down and I become a leaning forward over my ankles, and now I anti-shrug. Do you see what I did, Andrew?

I carry more weight. I'm showing you my triceps. If I organize that right, that can actually be a disc bulge reducing procedure. - Interesting, because when I had this L4 disc bulge, the suggestion to me was to do cobra pose or something similar, to lie down on the floor, point my toes out, so toes and tops of feet and legs are in contact with the ground, and then to push up and essentially to arch the spine, and then to repeat that, 10 or so cobra push-ups, as it were, and then to hold the final one for maybe 30 to 60 seconds, and then to get up and return about my day and to do that several times, and it worked fabulously well.

- That works fabulously well for certain types of disc bulges. We did experiments on this, and if the disc original height or 70% of that height or more is remaining, that works very well. If you flatten the disc so it's lost, it's about 60% or less of its retaining height, that won't work.

In fact, that will probably cause more pain, so that, it's called the McKenzie prone press-up or the cobra pose, can be very effective with the rider of how much disc height is remaining. But another concern occurs. Some people think, "Well, that was an effective therapy for that disc bulge for two weeks.

I'm going to do it every day for the next year." Now we run into a problem. The disc is now a little bit flatter. These facet joints on the back are two articulating joints. There's the motion that they're undergoing during the floppy push-up, as it's called. - The cobra push-up.

- The cobra push-up. Because the disc is now lost height, you've now biomechanically transferred much higher load to those facet joints, and they become irritated. So before, bending forward under load caused your pain in the disc bulge to grow, but now bending back causes pain from the facet joints, which is another distinctive pain.

We can arch back, drop one shoulder back, and, oh, yeah, you can feel that local ache there. So those are a couple of issues to be aware of. We did another experiment where we mimicked the floppy push-up versus simply holding it isometrically. And the isometric pose doesn't cause the movement irritation of the facet joints.

In terms of returning the disc bulge, it was just as effective. But following the same guideline again, 70% of the original disc height must be remaining for the isometric to work. So there's some guidelines for you to make that exercise even more effective. But you asked, what else could impinge on a nerve root?

Over time, as the disc becomes damaged, you now get more motion, and this is what we call an unstable joint. That causes more load on the facet joints. So let's do our do-si-do one more time. And this model has been prepared that this disc, the fourth lumbar four, is damaged.

L5 is normal, L3 is normal. This is the joint that has lost stiffness. Now people hear the word stiffness, and they think that's a bad thing. But a joint has to have a certain amount of stiffness to provide support and define the range of motion. So remember, this is the damaged joint.

I'm just going to apply a general torque above. And you see how the majority, the overwhelming majority of the motion is occurring at the damaged joint. Not at the one above and not at the one below. Now let's turn around and look at the facet joints. They've been painted red.

Those are the joints that are working because of the disc damage. So when we turn a little bit, we get a little bit of shearing motion. If we turn a lot, that joint, that facet joint on the compressive side is overloaded, and that causes the whole upper vertebra to slide across.

Over time, that's going to encourage arthritic bone growth just at that level. So another mechanism for the impingement on that nerve root is bone growth around the facet joint, which will make the hole even smaller. So there's another source of pain. The moral of the story is keep your discs as healthy as you can, and you'll have a better life.

Well, that's okay. So are there ever cases where one would want to attempt to return the disc to its proper compartment? In other words, to reverse or reduce the bulging of a disc where the proper movement would be the opposite of a Cobra push-up, where it would actually involve abdominal work in order to try and work back in the disc from the other direction, so to speak?

Yeah. "It depends," is the answer. There's a real nuance to all of this. So that's why we spend so much time on the assessment to define the precise nature of the disc bulge. And I should just mention that in the episode that we recorded with you, which we provide a link to in the show note captions, you described some of the assessment questions, self-assessment questions.

We talked about "Back Mechanic," your book, which fabulously describes some ways to self-assess and remedy, as well as a link to some of the clinicians that you've trained in the precise methods based on much of the work that you and others have done to address these problems specifically. Said long-winded, because as Dr.

Stuart McGill has pointed out many times, the sources of back pain are many and varied, and the relief for back pain is both highly individual and involves varied techniques, depending on the nature of the injury or the nature of the pain. And there are a number of other factors, psychosocial, emotional, et cetera, that are also important.

And we describe all... I should say Dr. Stuart McGill describes all of those in the episode linked in the show note caption. Yeah. There's a time for surgery and a very specific type of surgery. There's a time for a very specific type of exercise, be it mobility, stability, or whatever.

There's a time for pretty much everything. The key is to match it to the... I don't want to say injury, but it could be an injury. It could be a sensitivity, et cetera. But anyway, going back to this idea of there being a... That is now called a clinical instability that you can see.

If you could arrest that joint and restore its motion, so when you twist, the whole unit doesn't see the shearing joints, you do that through abdominal contraction. So if I cued you and said, "Andrew, push my fingers out," yes. Don't push your belly forward if you can. Try and flare your oblique muscles out laterally.

That's the pattern. And that will then arrest that micromovement and some people will... That will say it takes their pain away. Is there ever a time to flex forward to deal with the disc bulge? And the answer is yes. The type of disc bulge that when you bend forward and the disc bulge is on the back of the disc is typical of a weight training kind of injury.

If you had someone with a very flexible spine, they don't lift weights, but they do lots of yoga. Backbends. They've adapted their spine for mobility, not for load bearing. So the collagen and the ground matrix between the fibers have become very soft. So whereas someone who was strength training, when they squeeze and bend forward, the disc bulge comes out posteriorly, someone with very soft constituency to the disc, it bulges on the front.

So it's a different type of bulge. So it depends on how you've adapted your spine as to whether flexion will help you or extension. So again, knowing with some precision, the mechanism of the pain or disorder allows you to match the intervention. Fantastic. Well, this has been a wonderful description of spinal and pelvic anatomy discs and a very dynamic structure and yet a very stable structure in its best configuration.

What amazes my students is when I hand them a spine and I get them to with all their strength, try and bend it and break it. They can't. So it's incredibly robust. But the things that we do to ourselves, creating long levers and doing what we do creates tremendous internal stress concentrations beyond what you could ever apply with your hands.

All the more reason to do the McGill Big Three on a regular basis that was also described and demonstrated in some other videos that we provide in the show note captions. And of course, please be sure to check out the full length interview with Dr. Stuart McGill in which he describes in beautiful and immensely clear detail the structure and function of the spine and back, how to strengthen your back, how to get rid of back pain and how to stave off back pain, not just after an injury, but your entire life.

And by the way, at this moment, he is 67 years old. He's in awesome shape and an inspiration to me and anyone watching, I'm sure is equally impressed that he puts in the work on a regular basis. And in that episode, he also describes his so-called biblical schedule, which is six days a week of fairly limited in duration training geared toward cardiovascular fitness, strength and mobility.

It also includes a full day of rest.