Basic muscle function

The three main systems that drive human performance are the central nervous system, the muscular system and the skeletal system. While these are all independent systems within your body, they must operate interdependently in order to program successful movement patterns.

The central nervous system (CNS) works to feel what is happening in your operational environment so that it can select the appropriate muscles to create movement, this is proprioception. The CNS will sense what is happening around your body so that it can program the appropriate muscles to create a reaction. An example is being able to feel the difference between running on hard asphalt and running on loose dirt. Your body needs to work a lot harder on the dirt because your CNS can detect the fact that it is unstable, so more muscles will be recruited to help your body maintain stability. The less stability you have in your training environment, the more muscles will be needed to create and maintain stability for your body.

The muscular system is comprised of striated skeletal muscle. Muscles do one of three things: shorten, lengthen, and tear. For the purposes of educating you on how to develop a successful exercise program so that you experience results, we will focus on the first two in hopes of avoiding the third. All of the information written about exercise comes down to the fact that muscles will not shorten or lengthen unless the are told to by the CNS. In order for movement to occur, while on set of muscles shorten, the opposing set will lengthen in order to allow movement to happen. Muscles, and the tendons which attach them to the bones they move, are very elastic and are designed to stretch, much like a household rubber band (keep this in mind because this analogy will be used later on to describe how certain muscle actions work).

When a muscle contracts, or shortens, that is a concentric muscle action. When a muscle concentrically contracts, it produces a force to overcome a resistance while at the same time working to accelerate that resistance. So a concentric muscle contraction can be thought of as an overcoming muscle action, or an accelerating muscle action. Think of a bicep curl; as the biceps brachii shortens (goes through a concentric muscle action) it produces a force that overcomes the weight in your hand while at the same time accelerating that weight from a position of rest to movement through the ROM of the elbow joint. These three terms: concentric, overcoming, accelerating, will be used repeatedly to describe the same action: muscle shortening

When a muscle lengthens, it is performing an eccentric muscle action. When a muscle goes through an eccentric phase, it is yielding to the force of the resistance while at the same time working to decelerate the resistance. An eccentric muscle can also be a yielding muscle action. Think of the down-phase of a chest press; as the weight is lowered towards your chest (being accelerated by gravity) your pectoralis muscles work to decelerate the weight so that it doesn’t crash through your sternum. The muscles are working, but they are yielding to the force of the weight being accelerated by gravity. The three terms: eccentric, yielding, decelerating, will therefore be used repeatedly to describe the same action: muscle lengthening.

There is one more type of muscle action: isometric. Many people think of an isometric muscle action as one where the muscle does not change length. A better way to think about an isometric muscle action, as described by the late Mel Siff, is one where the muscle contracts, but the joint the muscle works does not go through a ROM. In order to experience this, take your hands, push them together in front of your chest, you can feel your chest and tricep muscles shorten, but the shoulder and elbow joints are not able to successfully go through a ROM. When isometric muscle actions occur, they primarily work to stabilize one joint, so that another joint can go through a ROM. The terms: stabilization or isometric, will be used to describe a concentric muscle action where a muscle shortens, but the joint that muscle is attached to does not move.

The skeletal system is nothing more than the support or structural system for the human body. This support system if comprised of bones that make up the frame. The intersection where two bones meet is a joint. Some joints are designed to move, for example the hip-which is a ball-and-socket joint; while other joints-the sutures of the skull, are not. Ligaments connect bone to bone, and are pliable, yet, unlike muscles and tendons, are not designed to lengthen.