1. Muscles
 Muscles work in opposition to one another
i.e. as one muscle is contracting the other
muscle is relaxing.

2. Muscles in Opposition
Deltoid – Latissimus Dorsi, Pectoralis Major
Ilio-psoas(hip flexor) – Gluteus Maximus
Biceps – Triceps
Quadriceps - Hamstrings

3. Classification of Muscles
 Muscles can be classified according to the part they
play in a movement.
 Here are four classifications of muscles:
1. Protagonist
2. Antagonist
3. Synergist
4. Fixators
 For this course we will only concentrate on
Protagonists and Antagonists.

4. Muscles - Protagonist
 Protagonist – a
protagonist is the muscle
which is the prime (main)
mover of an action
 E.g. The biceps is the
protagonist in the action of
flexing the elbow joint.

5. Muscles - Antagonist
 Antagonist – An antagonist
is the opposite muscle to
the protagonist. As the
protagonist contracts the
antagonist gradually
relaxes.
 E.g. As the biceps contract
the triceps gradually relax
and controls the movement.

6. Muscles - Antagonist
 Antagonist – An antagonist
is the opposite muscle to
the protagonist. As the
protagonist contracts the
antagonist gradually
relaxes.
 E.g. As the biceps contract
the triceps gradually relax
and controls the movement.