Core Talk: The Trunk

This is the final post in the “Core Talk” series. I saved this one for last because everything we have talked about up to this point, ultimately, should tie back into the trunk. It is a simple analogy, but think of a tree and its trunk. The branches anchor into the trunk of the tree. Without a strong, healthy trunk, the branches will not be able to withstand the elements. An unhealthy tree trunk will cause the branches to not be as healthy. The trunk has the potential to affect any and all of the previous regions we have talked about. Without an efficient trunk, the rest of your body will not be as efficient as it could be!

When treating someone for a shoulder issue, it is important to treat any dysfunction in the trunk as well, and ultimately tie (or re-integrate) the shoulder back into the trunk. Same for the foot/ankle, neck, or hip; to fully help someone to the best of our ability as clinicians, we need to help them to re-integrate the different regions and systems that are symptomatic back into their “center,” the trunk.

So let’s define the trunk and what efficient vs. inefficient looks like!

THE TRUNK DEFINED

For the purposes of this post, we will define the trunk as anything that is not an arm or leg or neck. That means the pelvis, lumbar spine, abdomen, rib cage, and thoracic spine would be included. This is the area that most people will probably think of when some one says “core.” But as we have already talked about in previous posts, we have “core” muscles all over our body. To review, these are the muscles that are usually smaller and have a stabilizing role. They are meant to work for longer periods of time and not usually for large movements, but should fire before this big movements happen. Some of the more known core muscles here would be the abdominals (obliques, transverses abdominus,), deep hip flexors (iliopsoas), pelvic floor muscles, deep back extensors (multifidi, quadratus lumborum), diaphragm (yes! that muscle that is important in breathing!), and more.

EFFICIENT TRUNK VS INEFFICIENT TRUNK

An efficient trunk is one that is able to move through all ranges of motion with ease and no pain. It has the ability to AUTOMATICALLY engage/fire/recruit without you having to “tell it.” Efficient function of all aspects of the trunk help to create increased pressure in the abdomen and thorax. This is part of how we create stability. For example, when you go to lift your baby, or a back pack, or a bag, you do not think, “tighten my stomach and then lift.” You just lift it! If your trunk is functioning efficiently, then it will have fired to stabilize you before you ever began to lift. This is how our bodies were designed to function! What an amazing design! To take it even further, when you went to lift that baby or box, or back pack, your trunk would have fired, your shoulder girdle core muscles should have fired, your neck core muscles should have fired, and even your hip/knee and foot and ankle core muscles would have fired! They all worked together! And they all needed your trunk to be engaged to be at their best!

An inefficient trunk is one that is limited in one or more ranges of motion, has pain or discomfort, and is unable to engage/fire/recruit automatically when a demand is put on it (great or small.) When inefficient, the trunk will not be able to create the increased pressures that are required for stability. If we take the same example as above. If you go to lift your baby, or a back pack, or a box and your core is not firing automatically, then you will inevitably have more stress placed on your shoulder girdle and/or neck due to increased work they will have to do with less support from the trunk. Do this one time, and it may be no big deal. Do it over and over again, and you have a greater risk of injury. (Of course this is not guaranteed that you will be injured from something like this, as people lift poorly all of the time!. But, physics says that poor mechanics will increase strain to your tissues, and increased work will increase strain on your tissues more than a lesser work load would.)

THE SODA CAN ANALOGY (A BRIEF INTRODUCTION TO THE PRESSURE SYSTEMS)

More than just muscles are involved in creating the strength and stability at the trunk. I would be remiss not to mention the pressure systems. This is a very brief explanation of how the increased pressures created increase stability.

Imagine that your trunk (and the muscles in it) are a cylinder, like a soda can. The pelvic floor muscles are the bottom, the abdominals and lower back muscles are the sides of the can, and the diaphragm is the top (though we could take it further and talk about how the vocal cords may actually be the top! But maybe in another post). With a soda can, if it has not been opened, then there is a certain amount of pressure inside the can that makes that can very strong. One could stand on it and likely not crush it. Now, open the can, or keep it closed and put a dent in the side. If one tries to stand on it now, it will be easier to crush. This is partially due to the pressure in the can being changed.

Now apply that to the body. When all of the muscles of the trunk contract together, in synergy, it creates increased internal abdominal pressure. This is part of creating stability. (There is much more to this, but for the purposes of this post, let’s stop there.) When this function is efficient, you will feel stronger and be stronger. Your body can withstand more stress and work without breaking down or becoming injured.

When this system is not efficient, this increased pressure is not created as well, creating less stability and potentially increasing stress to other areas of your body. We will get more into this in a separate post. For now, understand that there are multiple “players” in the trunk helping to create efficiency.

I hope you have enjoyed, and learned something, with our latest blog series. Feel free to comment and ask questions! And if you have anything (suggestions) for future posts that you would like us to touch on or questions you want answered, let us know!