When a muscle length stays constant while contracting to hold a position, which contraction is occurring?

• A. Concentric contraction
• B. Eccentric contraction
• C. Isometric contraction
• D. Cocontraction

Answer: (C)

Isometric contraction is when a muscle generates force without changing its length, allowing you to hold a joint in a fixed position or stabilize it. In this scenario, the muscle stays the same length while contracting to maintain a posture, which is exactly what an isometric contraction does.

Concentric contractions shorten the muscle as it produces force to move a joint, while eccentric contractions lengthen the muscle under load as it controls movement. Cocontraction involves the simultaneous activation of opposing muscles around a joint, which can also stabilize a position, but the defining feature here is that the muscle length does not change—classic isometric action.