The Complexity of the Spine

Low back pain, and other such injuries are all too common in the sport of dragonboating. Below is a fairly detailed essay on the spine, its related structures, and relevance to this sport. It is quite dense, but I do my best to make this piece as accessible to as wide an audience as I can.

The piece is broken in 4 sections:

  1. Orientation & Surrounding Structures (anatomy heavy)
  2. Intro to Cervical, Thoracic, and Lumbar Spine (kinesiology heavy)
  3. Why All This is Relevant and Differences Throughout the Spine (application)
  4. Conclusion (final thoughts)

Lastly, there are 4 “Check-ins:” throughout the piece. Use these as mental breaks, rest stops, thought pieces, and checks for conceptual understanding. Some questions are straightforward, while others are more challenging.

 


Post Objectives

  • Orientation of the spine
  • Overview of articulating structures, discs, muscles, and nerve roots.
  • Compare and contrast basic components of the cervical, thoracic, and lumbar spine.
  • Demonstrate how structural differences within each vertebrae will influence our movement.
  • Highlight relevance to sport of dragonboating

Orientation & Surrounding Structures

Overview

Spinal Segments.JPG
Fig. A

The spine is our “backbone”, which consists of numerous lego pieces called vertebrae, and sits in the pelvis (sitbone). To orient ourselves, let’s first refer to Figure A. From left to right, we have an anterior- frontal view (imagine looking at a person face to face); a sagittal view from anterior to posterior (someone standing sideways, but facing the left); and a posterior-frontal view (standing directly behind someone in line in elementary school, waiting to go out to recess).

There are several named sections of vertebrae grouped by function, structural differences, and embrology – 7 Cervical, 12 Thoracic, 5 Lumbar, 5 “fused” Sacral (essentially one bone), and 3-4 fused Coccygeal segments known as the coccyx.

Within our vertebral column (spine) lies an extension of our brains – the spinal cord. This structure gives way to our nerves for both sensory/motor feedback and control, exiting through various levels of the spine.spinal cord.JPG

Curves

In addition, as seen in Figure B below, each part of the spine (cervical, thoracic, lumbar, etc.) holds a different Anterior to Posterior (front to back) curvature.

 

Spinal Curvature
Fig. B

 

 

The different curves provide rigidity/stability, while giving us mobility to move in different directions. The curves also allow us to better absorb various loads. (For reader’s knowledge/reference: the cervical spine holds a lordodic curve, the thoracic spine – kyphotic, lumbar – lordodic, and sacral/coccyx – kyphotic).

Check-in #1: Why isn’t our spine shaped like a straight rod, would this not give us maximum rigidity? On the contrary, why doesn’t our spine just have one curve to provide flexibility?

Discs, Nerves, Ligaments and Musculoskeletal Structures

This section isn’t necessarily important for the overarching premise of today’s post, but I would be remiss to not mention the clinical and day-to-day relevance of the structures in this section. If you are pressed for time, skip ahead to the “Intro to the Cervical, Thoracic, and Lumbar Spine”.

If our vertebrae were just stacked one on top of another, that would be very uncomfortable, and we’d live our lives with constant bone on bone articulation, which is definitely less than ideal.

Luckily for us, we have something called intervertebral discs that are wedged inbetween each vertebrae.

nerves and disc
Fig. C

As illustrated in Figure C, discs serve to support the spine, absorb, and redistribute forces. In Figure D, The two cylindrical shapes sandwiching the translucent space represent the two vertebrae, and the middle portion illustrating the buoyancy and function of the discs.

disc-movement.png
Fig. D

 

So, how do we sense changes in movement, receive sensory feedback, and things like pain? Introducing, nerves.

nerves comic.jpg

Nerves are essential for both sensory and motor control, and often (thoughtlessly) tied to LBP. The nerves and their roots that innervate and modulate our actions/reactions exit through the spinal cord. Nerve intrapment or impingement therefore could cause a lot of discomfort, loss of sensory/motor function, and pain.

intervertebral foramin
Fig. E

The nerves exit through the Intervertebral foramen shown in Figure E, while the spinal cord traverses the Vertebral canal down the spine.

Certain movements can place additional stress to the discs and nerves, unbeknownst to the everyday joe, athlete, or paddler, and is often on the forefront of differential diagnosis for a clinician.

Last little bit for this section: there are numerous muscles and ligaments that support the spine that I will save for another post. With numerous layers in muscularture providing movement/stability, despite what some people might think, our backs are one of the most protected areas of our body.

Below is a transverse cross-section of our lumbar spine (imagine laying down on your back and taking your hand, and making a horizontal cut across your body and being able to look down from a “birds-eye view”), for reference.

back stabilizers and layers

 

We will now shift our focus to the intricacies of the Cervical, Thoracic, and Lumbar spine.

Check-in #2: If somebody has an impinged nerve on the left side of their body, do you expect to see them shift their torso to the left or the right?


Intro to the Cervical, Thoracic, and Lumbar Spine

cervical thoracic lumbar

While there are many parts of the spine, the cervical, thoracic, and lumbar are responsible for most of our spinal movement. These regions represent the neck/upper back, upper-mid back, and low back respectively.

Basics

Remember, there are 7 Cervical vertebrae, 12 Thoracic, and 5 Lumbar. Each vertebrae is named in sequential order. So, C4 in the picture above refers to the 4th Cervical vertebrae – meaning that there are 3 other vertebrae above, and 3 other cervical vertebrae below.

When we talk about motion in the spine, we need to describe what a motion segment is, define how each vertebrae articulate with one another, and delineate the general osteokinematics (different motions available), .

First, let’s look at a single vertebrae.

Single Vertebrae
Fig. F

The vertebrae on the left is drawn from a transverse view, while the one on the right depicts a sagittal view. The pointy prominance in the middle is named the spinous process. It is the inferior-posterior-most aspect of the vertebrae, and could be used to orient yourself whenever you look at the spine. The body is always in front of, or anterior, to the spinous process.

I want to focus your attention to the structures circled in red, called facets. These structures, when articulating with vertebrae above and below are called “Facet Joints” (also, zygapophyseal or apophyseal joint). Each vertebrae has two sets of facet – one set superior, and the other inferior. One set of facet consists of two surfaces, one on each side.

motion segment

The superior facets of one vertebrae, say L3 for example, interact with the inferior facets of the vertebrae above, L2. The inferior facets of the same vertebrae, L3, articulate with the vertebrae below, L4. Thus, two successive vertebrae and its surrounding structures constitute a motion segment – where the respective movement available at that vertebral level is determined by the orientation of the corresponding facets.

Thus, because of these facet joints, the general movements that a motion segment allow are as follows:

osteokinematics of spine

If you don’t follow the table, no sweat. Start by ignoring the middle two columns and focus on the left and right (Common/Other terminology). Essentially, because of your facets, you can move

  1. forwards and backwards (flx/ext) 2. side bend to the L/R (lateral flx) and 3. Rotate left and right (axial rotation)

Check-in # 3: Guess/name one reason why we could rotate so much at our neck and much less so throughout the rest of our back?


Why All This Is Relevant and Differences Throughout the Spine

If you’re sick of all the anatomy and kinesiology up to this point, it’s ok. Imagine doing this for 3 years intensively and subsequently the rest of your life!

If you’re just in love and in awe with the anatomy and kinesiology explained thus far, that’s also ok. Imagine being able to do this for the next 3 years intensively and subsequently the rest of your life!

Hang in there, we’re in the home stretch!

Remember everything you just learned about facet joints and how they are determinants of movement? Well, hopefully this next section helps explain “Check-in #3”, and why desired movement patterns come easier for some paddlers than others!

Cervical v. Thoracic. v. Lumbar

Aside from the change in curvature along the spine that differentiates cervical, thoracic, and lumbar segments, the orientation/angle of the facets at each vertebrae also play a huge role in the function of the respective segments.

In other words, the cervical, thoracic, and lumbar spine’s facets face different directions. The facets therefore don’t just influence motion, rather they dictate varying types of movement at different parts of the spine.

facet angle and orientation.jpg

It may be hard to tell from the picture above, but the general rule of thumb is that cervical spine facets situate at a 45° angle, like an inclined surface/slide. The thoracic facets incline even greater, at a 15° angle, almost straight up and down. The lumbar spine, angle outwards at 25°, but orient in a inwards direction, facing the spinous process, unlike the cervical and thoracic facets that orient upwards and towards our backs.

Thus, each region of the spine is better at certain movements than others.

Because of the direction of the facets, these are the motions most available at different parts of the spine:

Cervical: Flexion, Extension, Rotation, Side-Bending

Thoracic: Flexion, Extension, Rotation, Side-Bending

Lumbar: Flexion, Extension, Rotation, Side-Bending

*Bolded indicates primary movements at particular spinal level.

Remember, this isn’t to say that you absolutely do not have a certain type of movement at a certain segment of the spine, rather, certain motion is much less available and difficult at certain parts of the spine than at others.

Also, there isn’t a sudden difference in facet orientation at each cervical, thoracic, and lumbar junction, rather there is a gradual change in orientation of the facets that allow for smooth transition of movement from vertebrae to vertebrae.

Relative Motion
This image illustrates that at higher thoracic levels, there is more rotation available than at lower thoracic levels. However, at lower thoracic levels (mid-low back), there is more flexion/extension available. Ability to side-bend (lat. flexion), more or less stays the same.

 

 

More On Movement + Compensations

I do not mean to insinuate that motion occurs soley in one plain or direction at a time. In movement, sports, and life, rarely do you just bend forward, or just rotate, or just lean to the side. When a basketball player continuously dribbles a ball between their legs, their spine will often go from a relatively flexed position to a standing position, while their spine goes through some rotation. When you pick something up, you bend from the hips, and sometimes rotate to bring yourself closer to the object.

rotated and flexed.JPG
Coupled motion of the Spine – Flexion + Rotation, Rotation + Side-bending.

This phenomenon, called coupled motion, is particularly evident in dragonboating. In most of the stroke, you are in a forward-flexed position, coupled with spinal rotation. Another example of coupled motion is unintentional side-bending to one side that is accompanied with rotation. This can help explain why an athlete that is asked to not derotate as early during the pull, sometimes can’t help but to collapse and sidebend as a compensation if the rotation can not be held.

Model Paddler
Fig. G, Uncompensated Kinematics, 2016 CDBA College Cup

Looking at Figure G, it is safe to say that overall, his attack position is what we desire to see from our athletes – at least in regards to quality of movement from the spine. Recall, a healthy spine that moves as the facets were meant to move will have the ability to flex forward in the low back (lumbar spine), rotate in the upper thoracic (upper-mid back), and extend his head upwards (cervical spine), so that he could see the strokers ahead. Stability in this position, and the ability to efficiently translate your power throughout the stroke is what helps accelerate the boat.

More often than not, however, paddlers will not be able to hold these positions throughout the stroke. Even when athletes, such as the paddler in Fig. G, are able to find the desired position at the catch, their bodies will find ways to compensate during the pull, much like the paddler in Figure H below.

Compensated Paddler
Fig. H – Compensation, excessive flexion in thoracic spine

Differing athletes, for different reasons will have different capacities and control of the available movement afforded to their spines. Some considerations involving movement dysfunction, changes in range of motion, and strength at the spine include musculoskeletal injury (muscle/ligament sprain/tightness/soreness/fatigue), protection against neurological and discogenic symptoms (nerve/disc pain), restriction of movement in the facet joints, and lack of motor awareness/control.

For example, in Figure H, although her positioning can be attributed to a number of things (inability to associate arm movement with downward movement of spine, etc.), let’s assume that there is a spinal movement dysfunction and that her attack position was the same as the paddler in Figure G. To go from the attack phase to her catch/pull, the athlete could simply bend forward and lower her arms simultaneously from her lumbar spine to help approximate the blade to the water. But, if there is a facet restriction in the lumbar spine, low back movement in flexion and extension will be limited.

Where there is a restriction – there is a way. The body will simply move up and down the chain to the path of least resistance in an attempt to facilitate the desired motion wherever it can be achieved. The result? The blade is successfully buried into the water for the duration of the pull. The cost? An excessively flexed thoracic spine (upper back) that also detracts from the athlete’s ability to maintain rotation.

Before Intervention: Restricted Facet -> Lack of lumbar flexion -> Compensation upstream -> Path of least resistance -> Flexion from cervical and thoracic spine -> Reinforce undesired movement patterns.

After Intervention: Restore motion/mechanics of facet -> Restore healthy lumbar motion -> Path of least resistance -> Flexion from lumbar spine -> Focus on side-bending/rotation in thoracic spine -> Reinforce desired movement patterns.

Earlier, I brought up the example of a paddler who collapses on their side excessively during the pull instead of maintaining the desired rotation. This too, can be attributed to a restricted facet joint, using side-bending as opposed to rotation as the preferred method of motion due to its lack of resistance to movement.

Check-in #4: A paddler who has trouble rotating is not responding well to verbal cues. What tools can you use to help the athlete learn execute the stroke? What are some possible contributing factors to the movement dysfunction?


Conclusion

It can often be frustrating for both the coach and athlete when both parties don’t understand why certain movements come so much easier for some paddlers, while others seem impossible to change. Some of coaching comes from exposure to teaching techniques, some of it from science, and all of it from mutual trust and communication between coach and athlete.

The other thing to be aware of as a coach is, what are you asking of from the individual athlete in front of you? If you are asking them to get their blades deeper into the water, no doubt that eventually they will do so. The question is how. Each athlete will employ different strategies, based on their mobility and control of their bodies to attain the perceived desired results that the coaches request. If you look at their blades in the water  after repeated requests- yes, their blades are now fully buried. But the next question should be, what compensations or movements did the person have to make to get to this position, and why was it so difficult for them to get into the position in question in the first place?

While my last two examples in the section above detailed how facet orientation and restriction in these joints can affect performance outcomes in paddling, I want to reiterate that structural anatomy is just one of many factors that can influence movement and pain. Not everything is as black and white or as clear as it seems. Musculoskeletal injury (muscle/ligament sprain/tightness/soreness/fatigue), protection against neurological and discogenic symptoms (nerve/disc pain), restriction of movement in the facet joints, lack of motor awareness/control, environmental, and psychosocial factors all play a complex role with both movement quality and low back pain.

This post details the structural anatomy of the spine, in hopes of outlining just how involved movement analysis, rehab, and sports performance can be. I also hope that this piece serves as an educational space for those who are interested in the sport of dragonboating + kinesiology, whether you are an athlete, coach, or fellow health care provider.

The goal for everybody should be longevity in their respective fields and sports.

Hopefully this provides one step towards that direction.

Bryan


References

Neumann, DA. Kinesiology of the Musculoskeletal System. Mosby, St Louis, 2002

Netter, F. H. Atlas of Human Anatomy, Philadelphia, PA: Saunders/Elsevier. Harvard, 5th Ed., 2010

Pawlowsky, S. PT 742 – Thoracic Spine Lecture. UCSF/SFSU Physical Therapy, 2018

Wanek, L. PT 706 – Structure, Function, Motion of the Spine Lecture. UCSF/SFSU Physical Therapy, 2017