Basic Kinesiology: Muscles Actions

The three types of muscle contraction are Isometric, Isotonic, and Isokinetic:

Isometric is defined as that type of contraction where muscle tension and muscle length remain constant. This type of exercise provides muscle strength gains but only at the joint angle held during the exercise.
Isotonic contraction is defined as that where the muscle tension remains constant and muscle length varies.
Isokinetic contraction is defined as varying tension and length.

In each exercise there are four main functions of the associated muscles, Agonists (prime movers), Antagonists, Stabilizers and Assistors:

The Agonists is generally the muscle we are exercising.
The Antagonist is the opposing muscle and acts in contrast to the agonist.
The Stabilizer muscles are those that hold a joint in place so that the exercise may be performed.
The Assistors help the Agonist muscle doing the work.

The stabilizer muscles are not necessarily moving during exercise, but provide stationary support.

To continue, click here: Basic Kinesiology: Agonist / Antagonist Muscles