The human body is an amazing thing. I’m in awe of it on a daily basis and how it allows us to move with enough chemical reactions to overload a large computer many times over – each minute, continuously for our entire life. Just to take stock, you have over 640 muscles and roughly 230 joints (depending who you ask). Your one foot alone contains 26 bones and 33 joints. Your spine contains 31 pairs of nerves, each terminating in a huge amount of innervations in order to relay information all over the body, not only to the muscles, but to all of your organs as well. So every time you take a step, there is a lot of stuff going on. Obviously I’m not going to write about everything that makes us move, because textbooks have been written on that subject so covering it with a blog article is a bit ambitious. What I would like to talk about is the concept of joint movement and how the levers and pulleys work in order to move your body from place to place.
Movement begins with a thought that “I’d like to take a step”. I’ll use this as an example because walking is something we do without thinking about it. A sympathetic nervous system response is initiated by our hormonal system, specifically something called a catecholamine, which are derived from the amino acid tyrosine. The ones that are involved in smooth muscle contraction are called noradrenaline and adrenaline. These hormones bind with receptors and initiate a contraction of smooth muscle. Now, there is a lot more that goes into it than that but the point I’m trying to get across is that our hormonal system is actually what controls the basic mechanisms of movement. There are some serious hormones that come into play while the body is trying to function, but let’s leave this discussion at that level and move on.
By initiating a contraction of smooth muscle, the brain fires a message down the spinal cord to the nerves that control contraction of the muscle in question (the foot in our example). There are 31 pairs of spinal nerves, each coming out of a level of vertebrae from the dorsal (back or posterior) and ventral (front or anterior) roots. The dorsal roots carry messages towards the brain and spinal cord, and the ventral ones carry them away, towards things like muscles and glands. These efferent nerves carry the signal down to the somatic motor neurons which cause the muscles in question to fire and contract. The interface between the motor neuron and the muscle fiber is called the neuromuscular junction and is crossed by neurotransmitters, much like an electrical pulse crosses a current line. The most common neurotransmitter when it comes to muscle contraction is called acetylcholine. There is a long process of contraction, which again I won’t get into in full detail here, but it is usually in response to the type of force that is being required and if you are taking a step, there is a concentric contraction and the muscles shorten up, prompting the joints to move.
Just in order to lift your foot, your body has to relay information all the way down your leg and into your back. When your body moves a joint, it affects every muscle that crosses over that joint, who have to contract concentrically as an agonist, or eccentrically as an antagonist. When one contracts, the other relaxes and then vice versa in order to return the muscle back to the start position. So just as an example of major joints, to take a step you need to contract your hip, knee, ankle and many joints in the foot, never mind the smaller joints in your lower back in order to stabilize your pelvis. There are 12 muscles alone that cross the knee and are involved in knee flexion and extension, so you can imagine how much is involved just by moving this way. Some muscles, like the rectus femoris, cross over two joints and help out a bit more. So imagine a rubber band pulling on a rod and moving it from one angle to another. One concept that a lot of people don’t understand is that muscles don’t move – they shorten and lengthen, but it is in the joints that the movement actually happens. By moving the end of one joint closer to another, all skeletal movement is created. Many things depending on what type of force is required to be generated can alter this. For example, taking a step forward is one thing. Taking a step up on a stair that is elevated requires not only a different amount of force generated by the joints, but also a completely different sequence of muscle contraction.
So why am I breaking this down for you? What I’m really trying to do is get across to you what an astounding cycle of events needs to occur in order to take a simple step. From the beginning of thought to just walking in sequence, we often take for granted all of the things that need to happen to do something very simple. In life we take many things for granted, and one thing I try to get across to all of my clients is don’t take your health, ability to move properly and how you live day to day for granted. With just one small alteration of this sequence – you will have trouble walking. The good news is that your body is constantly learning and turning over old cells and replacing them. It is constantly improving if you give it the tools to do so. We move all of the time without thinking about it. My goal is to get you to think about it. Only through that will you be able to really figure out how you should move properly. If you have any questions feel free to contact me.