First, a little about anatomical position. If you stand up, place your hands at your sides, and then turn your hands so that the palms are facing forward, this is the anatomical position. A good way to picture it is to think of your pinkies touching the seam of your pants. Later when we discuss muscles being on the "inside" or "outside" of a limb, this is the position we are starting from. When a body is in anatomical position, there are three "lines" that separate body regions. One cuts horizontally through the body at the belly button, dividing us into top and bottom (Superior and inferior). The other two divide the body vertically. One is aligned with our ears and shoulders and divides us into front and back (frontal and dorsal), the other splits us right down the line of our nose (Midline). The midline will become important when we start talking about how far away something is.
Once you divide the body, there are only a few more terms that we need to know in order to get started. Here is a list of the most basic:
• Proximal/Distal: These terms are used to describe how close something is to the midline (body division) in relation to something else. They mean how they sound--distal is more distant, proximal is closer (proximity). For example, if you compare your elbow to your wrist, it is proximal (closer than the wrist). If you compare it to the shoulder, it is distal (farther from the midline than is the shoulder).
• Medial/Lateral: These terms are used to describe whether a point is on the "inside" or the "outside" of something. For example, think of your foot. The big toe is on the medial (middle) side of the foot, and the little toe is on the lateral side.
OK! Are you still here? Good! Now we'll start looking at the fun stuff, muscles! In this first installment, we will examine the different types and shapes of muscles in the body, as well as the basics of what causes a muscle to contract.
There are three different types of muscles in the body: Cardiac muscle is found only in the heart; smooth muscle is generally found in blood vessel walls, and walls of organs such as the small intestine or stomach, etc.; the last is skeletal muscle, and this is the one that concerns us the most.
Skeletal muscle comes in four different forms, parallel, convergent, pennate and circular. Most of the msucles in the body are of the parallel type. This is where the fibers of the muscle lay mostly parallel to the long axis of the muscle. The biceps (Upper arm muscle) is a good example of this type of muscle. Convergent muscles are based over a broad area, but come together at one attachment point. The pectorals (Chest muscles ) are an example of this. They are broad near the center of the chest, but come together to attach at one point on the arm (Near to the shoulder). In a pennate muscle, the fibers all form a common angle with the tendon. These muscles don't contract as much as a parallel muscle will, but they provide more direct power. An example is the rectus femoris (part of the muscle group on the top of the leg known as the quads--it is responsible for straightening the leg at the knee). The deltoids (Shoulder muscles) are also pennate muscles. The last type is circular muscle. These muscles will not be looked at, since their function is to close openings in the body. The muscles that close the lips are examples of circular muscles.
Since what actually makes a muscle move and contract is an extremely broad topic, this will not be covered in detail. There are two nervous systems that we will look at, the central and the peripheral. The central nervous system includes the brain and nerves of the spinal cord. The peripheral nervous system contains the nerves that run out to the muscles and various parts of the body and then back to the central nervous system again. When the brain decides that a muscle needs to contract, it sends out a signal through the central nervous system. This signal passes to the peripheral system and keeps getting passed from nerve to nerve until it hits the muscle. The nerve at the muscle lets out a substance that causes muscle cells to contract. As long as the nerve lets out this substance, the muscle will contract (until either the nerve runs out of transmitter substance, or the muscle cell is completely exhausted). This sounds simple, but there are thousands of nerve and muscle cells that all need to act in unison to produce a contraction and a resulting movement.
That's about it for this session, in the next article we will start looking at specific muscle groups and how they relate to movement and their significance in triathlon. We will also discuss good exercises and stretches for each muscle group. Until then, happy tri-ing and good training!
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