I wrote this post about muscle function about 6 months ago. Have a read and feel free to comment. I’m going to follow it up with some updated thoughts, but I’d love to hear what you think 🙂
I want to preface the following comments with the fact that it is only my opinion. Part of the reason for writing this is that I have found doing this blog helps me clarify my own thoughts and muscle function is soooooo complicated, I thought it might help me get a grip!!
Muscles, their associated fascia and their action have always given me the impression I know nothing! The more I learn about them the more I feel I don’t know anything? I’m not talking about the mechanism for contraction or anything on a microscopic level…I’m talking about what is happening on a gross, activation/action level.
When you learn anatomy you are always told about the origin, insertion, etc. However, when it comes to muscle action you are always taught the concentric action and usually in the plane with the most movement. For example, the hamstrings extend the hip and flex the knee. This totally underestimates the potential of the hamstrings, there is definitely potential for the hamstrings in the frontal and transverse planes. Whether this is simply that the teaching of anatomy remains extremely traditional or because it is so difficult to scientifically prove what a muscle does in function that we’ve stuck to the traditional model of teaching. Whichever it is, I’m convinced we can teach a model of anatomy that translates to movement far better giving trainers/therapists a far better chance of understanding of function. I believe this is a major problem with the traditional teaching of anatomy; it is so abstract to how the body moves.
Having spent time learning to understand functional movement with Gary Gray, Dr David Tiberio and most recently/extensively with John Hardy I think muscle function is the hardest thing to understand, particularly if you come from a more traditional model of teaching. In our Diploma in Functional Therapy we go through every muscle…and we think about how it is loaded in all three planes. Recently, I talked about Fryettes laws of spinal motion, and then later that day John and I were chatting on the phone about muscle function, which made me think about the laws that might govern muscle function. I’ve never really read about any that cover what I am thinking about, so I started messing around with the following:
The Hardy-Poulton Laws of Muscle Function:
First Law of Muscle Function:
In function, muscles are activated through feeling force in one, two or all three planes.
Muscle can be activated by longitudinal forces, lateral forces, twisting forces or a combination.
Second Law of Muscle Function:
When activated significantly in one plane a muscle is more easily activated in the other planes.
For example, a small force in the frontal plane is more likely to cause a strong activation of the muscle if it has already been taken to end range in the sagittal plane.
Third Law of Muscle Function:
A muscle can be lengthening in one or two planes and shortening in another allowing it to maintain tension while still allowing joint movement.
Therefore, isometric muscle contraction* is rare in function, it is more likely that there is a trade off between the planes of motion.
* By this I mean no change in length of the muscle or its tendon. It is my belief that in function muscle fibres can often remain in a relatively isometric contraction in order to utilize the reactive nature of its associated tendon.
Obviously, this is only a model of what I think might be happening, as currently we cannot scientifically prove how muscles truly function during complex movements such as gait.
I don’t know all the answers on the best way muscle function/anatomy should be taught, but I think we can get to a model of teaching that allows the trainer/therapist to transfer their knowledge of anatomy to functional movement much more easily. The way we teach it is to not talk about a muscle in terms of its concentric action, this is ultimately misleading, even though it is not wrong.
The way we start is to think about how the local joint movement can turn on (lengthen) the muscle according to the above laws. We will do this in all three planes, for example, to turn on the gluteus maximus in all 3 planes you would take the hip through flexion, adduction and internal rotation. I think this allows you to see anatomy in movement straight away, showing how the anatomy can be applied…much more useful! Once you have done that you can start getting more complicated as your knowledge grows, integrating the role of fascia, the influence of distant joints and the effects of multiple joint movement.
For example, the soleus will directly affect the foot and ankle; however, by the soleus slowing the anterior rotation of the tibia during gait and the mass and momentum of the trunk taking the rest of the body forward over the fixed foot, the soleus will indirectly extend the knee. This type of muscle action occurs in many areas of the body with muscles influencing joints and body segments way beyond the joints that they actually cross. It also means that a muscle that crosses two joints is not as straightforward as one might think.
For example, the hamstrings are able to extend the knee in function and the peroneus longus can decelerate sub-talar eversion in spite of the fact that its concentric action will be listed as eversion in any anatomy book you look at. Have a think about these last two examples…it’s interesting, but it makes a lot of sense.
Research is happening all the time and as our knowledge and technologies progress we may get closer to understanding the complexities of muscle function, however, until then I think we will have to make do with a model of understanding that leads us to strategies of treating and training that work for our patients and clients.
I would love to hear your thoughts and comments on this post, you can comment on the blog or you can email me at firstname.lastname@example.org
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