1. Muscles and Movement

2. How Muscles Work A voluntary muscle usually works across a joint.
It is attached to bones by tendons.
When a muscle contracts, usually just one bone moves.
(EG: When the biceps in the arm contracts, the radius moves but the scapula does not).
TENDON

3. Origin and Insertion
(1)
The origin is where the muscle joins the stationary bone (1).
The insertion is where it joins the moving bone (2).
When a muscle contracts the ‘insertion moves towards the origin.’
(2)

4. Muscles Working in Pairs
Biceps contract
Biceps Relax
Triceps Relax
Triceps Contract
Flexion
Extension

6. Explanation
To FLEX (bend the elbow) the biceps contract (shorten) and the triceps relax (lengthen).
To EXTEND (straighten) the elbow, the biceps relax and the triceps contract.
This above is called an ‘antagonistic muscle action’.
The working muscle is called the ‘prime mover or agonist’.
The relaxing muscle is called the ‘antagonist’.
The prime mover is helped by other muscles called ‘synergists’.
These contract at the same time as the prime mover.
They hold the body in position so that the prime mover can work smoothly.

9. Tendons They connect muscle to bone.
They are white, flexible and very strong.
Tendons do not tear away easily due to them being embedded in the periosteum (surface of the bone).
If they do tear, it is often a long and painful recovery.

10. Muscle Shape and Size
Muscles come in many different shapes and sizes according to the job they have to do.
“Note the different shapes of tendons that go with them”.