Body Basics

Since you are going to act as your own coach and build your own marathon training program it will be very helpful if you have a basic understanding of how your body works and why it improves through training. Here is a brief and basic course in muscle and exercise physiology.

Muscle Basics

Every muscle in your body is composed of a well designed combination of muscle fibers, nerves, connective tissues and blood vessels. A tendon connects your muscle to your bone. When your muscle contracts or “shortens”, it pulls on the bone and produces movement.

Each muscle is made up of thousands of small individual muscle cells which are sometimes referred to as muscle fibers. Each fiber is a long tube like structure that travels along the entire length of the individual muscle. Imagine a large rope. The rope is made up of many small fibers. Each fiber individually is very weak and could be easily broken. But, there is strength in numbers. When the many individual rope fibers are joined together, they make up a very strong length of rope. Your muscles are very similar to this. Each individual muscle fiber is relatively weak. But, just as the rope, when many fibers are joined together you have a very strong muscle.

Each muscle fiber is essentially composed of a series of overlapping proteins. When a signal is sent to your muscle to contract or shorten, these proteins pull against each other, which result in a contraction of the muscle. That shortening or contraction of the muscle results in movement.

Your muscles are strong but they are also dumb. They won’t do anything unless you tell them to. You communicate with your muscle cells and give them instructions by sending a signal from your brain, through your network of nerves to a receptor at your muscle cell called a motor neuron. The motor neuron and the muscle cells that it controls is called a motor unit. Motor units comes in many sizes. It may control only a few muscle fibers or it may control hundreds. The force of the muscle contraction depends upon how many motor units are called into action. For instance the act of picking up a piece of cotton with your finger will use only a few motor units. Picking up a heavy weight or running at full speed uses many motor units. This process is important in understanding how your body strengthens and improves with physical training.

Muscle Fiber Types

All muscle fibers are not created equal. There are two basic types of muscle fibers that perform in different ways. This difference is of great interest to you as a marathon runner. One muscle fiber type is called fast twitch. A fast twitch muscle fiber contracts very quickly and produces a lot of power, but also tends to fatigue very quickly. Not an ideal type of fiber for a marathon runner! The other type of fiber is called slow twitch. This type of fiber is much more marathon friendly. It contracts more slowly and produces less power but is much more fatigue resistant. We all have both types of fibers in our body. The percentage of each type will differ from person to person. The percentage of each is genetically determined. It is something we are born with and, for the most part, cannot be changed. A world class marathon runner will likely have 75 to 98 percent slow twitch muscle fibers. In contrast, a top level sprinter may have 75 to 80 percent fast twitch muscle fibers.

As I mentioned, research has shown that you cannot change muscle fiber types, however, you can make your fast twitch fibers a little bit more resistant to fatigue with proper training. That is one of the reasons that you are able to run further without fatigue as you progress through your training program.

Fast twitch muscle fibers are not completely useless for a marathon runner. Far from it. Fast twitch muscle fibers come into use for your final kick to the finish line and when you accelerate to pass other runners. They also come into play when your slow twitch fibers become nearly completely fatigued towards the end of your marathon. One good marathon strategy is actually to increase your pace when you “hit the wall” in the last miles. Increasing your pace can bring fast twitch muscle fibers, that have not been used extensively, into play and give you a burst of energy.

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