Exercise Science Review 1-2, Eccentric, Concentric, and Isometric Muscle Actions

Posted by on Jan 11, 2013 in Exercise Science, Review Topics | 0 comments

There are three basic types of muscle action.  These actions are distinguished in a manner so as to separate the actions from the word contractionContraction implies shortening, and muscles can do all sorts of work, and sometimes some of their most effective (for muscle building at least) when they are acting against a force but not actually shortening.

They are distinguished by how great a force the muscle exerts relative to the external load.  There are three possibilities:

  1. Muscle Force > External Load
  2. Muscle Force = External Load
  3. Muscle Force < External Load

Most full body multiple join exercises involve muscles transitioning through all these actions.

Can you guess what happens to a muscle that exerts force that is greater than the external load?  It shortens.  This is concentric action.

Can you guess what happens to a muscle that exerts force that is equal to the external load?  It’s length stays the same.  This is isometric action.

Can you guess what happens to a muscle that exerts a force that is less than the external load?  It lengthens.  This is eccentric action.

 

Let’s give some examples.  The lowering phase of essentially any exercise is eccentric action.  The stabilization of the trunk muscles, abdominals, and erector spinae in the squat are examples of isometric action, and the upward movement of most exercises involves concentric action.

Make sense?  Post any questions you have to the comments.

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