Today we will focus on movement. So, lift your arm up. Wow, how did that happen? You just wanted to lift your arm up and it just lifted up. Can you explain what you did for that action to work so effortlessly? In most cases we cannot tell which muscles took part, or how did our mind communicate with the muscle, what else happened in our body so that the arm was lifted. Well, sometimes I like to think that I am magical in a way. We all are. But lets get serious for a bit bit, our movements also have biomechanical explanations.
How do we move our bodies? What happens in our tissues so that we move our limbs?
Fortunately we don’t need to know the mechanics of movement to move our bodies. The body and the mind is connected on many levels. And, our body knows what to do without any help from conceptual knowledge.
We think that our conscious mind is in control of everything. We also think that our unconscious mind activities need to be tamed by the conscious mind. But pause for a moment and really think about that. Take running for example. Imagine all the muscle movements that you need to engage simultaneously just for one step. I bet if we tried to do all that with our conscious mind we would barely be able to walk at a very slow rate. So no, our bodies are wise and we should acknowledge this wisdom rather than trying to control everything with our conscious minds.
So, today, we will focus on the anatomy of movement rather than exploring the conscious working of the mind.
Our bones, muscles and joints are the main elements of our body that functions in movement. They are all amazingly efficient structures. The muscles are key to anatomy of movement because they supply the force and direction for the movement.
The joints are the parts of our skeletal system where two or more bones come together. The connective tissue that hold our bones together is ligament. If two bones are connected together with very tight ligaments then we will get a joint but it might have a minimal range of movement like the Sacroiliac joint where the sacrum and the Ilium.
Sacrum the lower part of the spine just below the lower back (thoracic spine) and above the tailbone (coccyx); and ilium is the top broadest part of the hip.
But since we are focusing on movement today we will focus on the joints which have decent range of movement.
Joints has some other structural units in them to make it possible and easier for bones to slide over each other like the cartilage and the synovial capsule. Cartilage in the joint refers the gliding smooth edge of the bones, and the synovial capsule is the sac filled with fluid to ease movement and absorb shock.
To be able to move the bone or a limb we need a connection between the source of movement, i.e. the muscles, and the bones. The connective tissue that connects and transmits the force from muscles to bones is called the tendon. Our discussion here will focus on the muscles.
We have over 600 muscles in our bodies. The muscles we use in day to day movements are the skeletal muscles and they are usually under conscious control. There are other kind of muscles that our conscious mind cannot control, like the muscles of the heart and muscles of the internal organs. We also have some muscles that do not move, like the muscles in the skull which just stabilize it.
Alright a lot has been discussed but still we did not talk about how the movement occurs. What happens in the muscle so that it makes a limb move? If we want to understand the mechanism of movement the first thing we need to know is that muscles are composed of fibres and they can only contract. What this means is a muscle can only pull. They can’t push limbs away.
So, in general, if you need to find the responsible muscle for a certain movement you need to think about where a limb is going towards rather than the moving limb itself.
For example, think about the forearm. When you bend the elbow what happens is you pull the forearm towards the upper arm. The source of this movement can only be located in the upper arm rather that the forearm itself. The muscles on the inner side of the upper arm, biceps, shorten to pull the forearm bones towards themselves.
The muscles effect the bones they cross. The more stable and usually the more central end of the muscle is considered as the origin of the muscle.
From this origin the muscle crosses and attaches to another bone. In most cases when the muscle contracts the origin point stays stable and the ending edge gets pulled towards the origin point of the muscle. Some muscles only cross one bone so it is easier to find out the function of those muscles. But there are some muscles that crosses more than one bone and that will cause the muscle to have multiple functions in movement.
The muscles that cross just one bone is called the monoarticular and the muscles that cross more than one bone are called biarticular or polyarticular. For example the muscles that extends the hips (sending the leg back and up), also take part in the knee flexion.
Although muscle fibres can only shorten there are three type of muscle actions that are created through muscle fibre contractions. These three muscle actions are isometric, concentric and eccentric. In concentric movement the muscle shortens as expected. In isometric movement the muscle engages but without any noticeable change in the length of the muscle. And, in eccentric movement the muscle lengthens.
Now, the question is how can the muscles with fibres that can only shorten do more than shortening. Then let’s begin with isometric action of the muscles.
Imagine pushing against a wall or pulling an immovable object. In those situations your muscles engage but their length stays the same, nothing moves. In isometric contraction the fibres create an internal torque and an external torque. And these two torque forces cancel our each other with no visible difference in the muscle’s length. Although lengthening sounds even more impossible, the mechanism it refers to is quite simple actually. In eccentric contraction the muscle is already short, like bent elbow.
Imagine that you are holding heavy shopping bags in your hand and you want to put the bag down on the floor slowly. Although the action you need to do with your elbow is extension you use your elbow flexor for this action. Because of the force of gravity, if you relax all you muscles of your arm, then your arm will suddenly extend and you will crush the bag into the floor. To resist gravity in such a situation you engage the muscles you normally use to bend your elbows, elbow flexors, for extending your elbow slowly.
One other thing that needs to happen for us to bend the elbow is the relaxation of the triceps muscles located in the back side of the upper arm. The triceps function as elbow extensors. When we bend our elbow the front side of the upper arm shortens and the back side lengthens. If the triceps stay contracted then they will not let the lengthening to happen. This mechanism is called the reciprocal relaxation reflex. In case of the elbow when the biceps contract in order to flex the elbow the triceps has the potential to oppose movement. So the biceps and the triceps are the opposing muscles. In the opposing muscle pairs, the muscle that creates the action is called the agonist muscle and the opposing muscle that relaxes is called the antagonist muscle.
Although reciprocal relaxation of the antagonist muscles is a reflexive reaction it is still possible to co-contract the opposing muscles. The co-contraction of the opposing muscles creates stabilisation around the joint. During Asana practices we use this co-contraction mechanism to create muscular locks (Bandhas). By the help of muscular Bandhas we practice safely and actively protect and stabilize our joints. The whole muscle tissue wraps the bones of a joint creating a very strong posture.
As you can see even the simplest movements in the body requires amazing coordination within the body. Instead of a one simple movement, imagine dancing. Moving the body, in harmony with the music, using the torso, the head, the arms and the legs, the fingers and the toes. Moving them symmetrically, asymmetrically in orders to manifest a sensation, a feeling, a thought, through the movements of the body. Try rock imagine all those things that need to happen within.
And now tell me that we are not magical!