2. Role and Ranges of muscles
By: Dr. Abbas

3. Roles of Muscles The roles a muscle can assume are those of an:
Agonist
Antagonist
Stabilizer or fixator
Synergist

4. Agonist:
An agonist is a muscle or muscle group that causes the motion.
It is sometimes referred to as the prime mover.
A muscle that is not as effective but does assist in providing the motion is called an assisting mover.

5. Factors that determine whether a muscle is a prime mover or an assisting mover include
Size
Angle of pull
Leverage
Contractile potential

6. Example:
During elbow flexion, the biceps muscle is an agonist, and because of its size and angle of pull, the pronator teres muscle is an assisting mover.

7. Antagonist:
An antagonist is a muscle that performs the opposite motion of the agonist.
In the case of elbow flexion, the antagonist is the triceps muscle and biceps muscle is agonist muscle.
In the case of elbow extension, the triceps muscle is the agonist and the biceps muscle is the antagonist.

8. Stabilizer:
A stabilizer is a muscle or muscle group that supports, and allows the agonist to work more efficiently.
For example:
The abdominal muscles (trunk flexor muscles) act as stabilizers to keep the trunk straight, while the arms move the trunk up and down. A stabilizer is sometimes referred to as a fixator.

9. Synergist:
A synergist is a muscle that works with one or more other muscles to enhance a particular motion.
It is a term used to encompass the role of agonists, assisting movers and stabilizers.

10. Range of Muscle Work:
Range of muscle work is the extent of muscular contraction which results in joint movement.

11. Full range:
The full range in which a muscle work refers to the muscle changing from a position of full stretch and contracting to a position of maximal shortening.

12. The full range is divided into:
Outer
Inner
Middle range

13. Outer
range
Middle
range
Inner
range

14. Outer range:
Is from a position where the muscle is on full stretch to a position half way though the full range of motion.
Inner range:
is from a position halfway through the full range to a position where the muscle is fully shortened.
Middle range:
is the portion of the full range between the mid- point of the outer range and the midpoint of the inner range.