Sometimes it is confusing as to why we feel tight or have pain in certain areas and you may ask ” why the hell do I have pain there?” When dealing with chronic tension or pain it is important to eliminate as many stresors as possible and without some basic understanding of how muscles create movement that can be difficult. Hopefully this article will help you to understand the different ways a muscle may contract and help you to use your body more efficiently.
Muscles are specialized to shorten toward their center and this is contraction. There are 3 ways a muscle will attempt to shorten toward it’s center: concentrically, eccentrically, and isometrically.
A concentric contraction is when a muscle is successful in shortening toward it’s center and when this happens then one or both of the bones the muscle attatches to will move.
An eccentric contraction is when the muscle attempts to shorten toward its center but instead lenghtens. This happens whenthe muscle is trying to slow a movement down
An isometric contraction is when a muscle attempts to shorten toward its center and no movement happens. This would occur when holding objects.
Concentric Muscle Contractions
When a muscle contracts it pulls towards its’ center pulling on the bones it attaches to. It pulls in its line of pull and can move one or both bones.
Muscles are like ropes or rubber bands. If you look at the muscles and you see the lines those are the muscle fibers. The muscle fibers are the muscles lines of pull. So when that muscle pulls you can see which direction it would pull the joint or joints. When the muscles runs vertical it will pull in that vertical line. If it runs horizontal or diagonal it will pull in that direction. In this way you can look at any muscle and see what action it will perform if you remember that muscles always pull.
Slowing Down Movement (Eccentric Contractions)
Biceps brachii eccentrically contracts to lower the forearm
There are times when we want movement to be slowed down or controlled. In the example of the biceps curl, if the muscles did not control the movement gravity would bring our forearm down very quickly and slam the joints together causing injury.
In eccentic contractions the joint action that is occurring, the opposite muscle that creates that action would contract to slow the movement down. In the biceps curl the joint action that is occurring is extension of the elbow. The biceps brachii performs flexion so it would make a pulling force opposite of extension. In this way the muscle is lengthening while contracting.
Stabilization and Support Muscles
Here the trunk and neck are forward and the back and neck muscles isometrically contract to keep the head, neck, and trunk from falling forward
The biceps brachii crosses the shoulder and the elbow joint and would move both into flexion and the posterior deltoid stops that with a force of extension
There are times when muscles to need to stop unwanted actions or motion. This is termed “fixing” or stabilization. Usually gravity is a force that muscles need to stabilize against but another force that muscles need to stabilize against are other muscles. Most muscles have more than one action and when a muscle is directed to contract it attempts to perform all of it’s actions. This would not make for smooth movement. For example in a biceps curl we want to move only the elbow joint. One major muscle that would help with this is the biceps brachii. But the biceps brachii can also flex the shoulder which we don’t want to happen, so muscles that do the opposite action of shoulder extension would contract so that only flexion of the forearm can happen. There are literally hundreds of scenarios where this happens and this is called coordination because it is a “co-ordering” of muscles.
The weight of the bag exerts a downward force on the shoulder and to keep the bag on the shoulder the shoulder and neck muscles isometrically contract with an upward force
Another example of muscles stopping unwanted actions is gravity. When we carrying or lifting a weight on the left side of the body gravity would pull us to the left so muscles that pull us to the right would contract to counter that action. An easy way to remember it is any action we want to stop muscles that perform the oppossite action will contract. Stabiliztion movements are isometric contractions because no movement is occurring.
So we can see that in any movement any number of muscles will contract to make movement, to stabilize, and control movement. If you remember in the trigger points article that trigger points are one of the most common soft tissue problems it is easy to see why. Here is the link for more information on trigger points.
