Which muscle action produces tension while maintaining constant length?

• A. Concentric
• B. Antagonist
• C. Isometric
• D. Eccentric

Answer: (C)

Tension without changing the muscle’s length is an isometric contraction. In this type of contraction, the muscle activates to hold a position or stabilize a joint, generating force, but the length of the muscle fibers stays the same. You feel the effort as you resist movement or maintain a posture, like holding a plank or pushing against an immovable object.

Concentric contractions shorten the muscle as it pulls to move a load, while eccentric contractions lengthen the muscle as it controls lowering or resisting the load. The term antagonist refers to a muscle that opposes the primary mover, not a specific contraction type. So the described scenario—tension with no change in length—best fits isometric action.