Stabilizer
Short definition
A muscle that produces no driving torque but isometrically fixes a joint or body position, providing a base for agonists and synergists.
Full definition
A stabilizer holds a joint, body segment or posture still so that the moving muscles have a firm base and the correct trajectory. Without stabilizers part of agonist force is wasted compensating unwanted shifts. Stabilizers contribute a small share of total effort (typically 5–8%), yet their fatigue sharply reduces performance and raises injury risk. In the bench press the scapular muscles (rhomboids, serratus anterior) stabilize the shoulder girdle.
Examples
In the bench press the scapular muscles stabilize the shoulder girdle without moving the bar.