A muscle is able to adopt one of four roles. It can change between these roles instantly, and some muscles can function in all four roles at different times. The roles are:
1. agonist
2. antagonist
3. stabiliser
4. neutraliser
A muscle is said to be performing the role of a stabiliser when it's job is to hold a body part stable during a joint movement. For instance, when we walk, the muscles of the leg perform the main task of propelling us forwards, at the same time other muscles are holding the trunk steady, and are therefore acting as stabilisers.
Another example might be for when we do press-ups, the abdominals and hip flexors keep the body in a straight line and prevent it from folding inwards when we perform the press-up.
When a muscle fulfils the role of a stabiliser, it usually only has to shorten, or contract a very small amount, and it creates very little movement, if any.