Terre Pruitt's Blog

Muscles contract.  An isotonic muscle contraction is when the length of the muscle changes.  The isotonic contraction could be a concentric contraction where the muscle shortens or an eccentric contraction where the muscle lengthens.

As an example, your arm is hanging at your side, when you lift your hand to touch your shoulder that is an isotonic contraction.  Your biceps muscles are shortening, pulling your hand up to your shoulder in a concentric contraction, your triceps are lengthening in an eccentric contraction.  Lowering your arm the biceps muscles are lengthening in an eccentric contraction and it is actually your triceps contracting in a concentric contraction that is pulling your arm down.  But since gravity is helping the triceps don’t have to work very hard.

An isometric contraction is when the muscle contracts but the length of it does not change.  For instance, when you sneeze or cough. Your abdominal muscle contracts, but unless you bend into the sneeze/cough the length does not change.

To strengthen the muscles resistance needs to be added to the contraction.  Muscle must be challenged and learn to overcome the challenge in order to become stronger.  Tension/resistance needs to be added to movement/contraction.

There are many forms of resistance; gravity, weights, bands, tubes, immoveable objects (that you try to push or pull), all of it can assist in strengthening the muscles. 

The muscles can gain strength from both the concentric contraction and the eccentric contraction.  So lowering the weight after having lifted a weight toward your shoulder in a biceps curl can contribute to strength.

When the muscles contract in a concentric contraction they are pulling on bone. But that is not be be confused with a push workout or a pull workout.  Even when you are working your “pushing muscles” your muscles are actually contracting and pulling on the bones to complete the exercise.

Muscles contract, it is the added resistance that makes them stronger.