Question

An agonist muscle causes movement through concentric contraction and an antagonist muscle controls the movement through:

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

Hint:

The Muscle Action Duo: - Agonist (Prime Mover): Shortens its length ($\mathbf{\rightarrow \leftarrow}$) via Concentric Contraction to accelerate and drive the movement. - Antagonist (Opposing Controller): Lengthens its structure ($\mathbf{\leftarrow \rightarrow}$) via Eccentric Contraction to decelerate, stabilize, and smoothly control the joint action.

Answer 1

The Correct Option is B

Concept: Skeletal muscles perform coordinated movements across joints by working in complementary pairs: agonists and antagonists. The functional state of active muscle groups is defined by how the muscle's length changes relative to the internal tension it generates:
• Concentric Contraction: The muscle generates enough force to overcome external resistance, shortening its total length as it contracts (e.g., lifting a weight).
• Eccentric Contraction: The muscle generates tension while actively lengthening against an external load (e.g., controlled lowering of a weight).
• Isometric Contraction: The muscle develops active structural tension but stays at a constant length because the external resistance matches the muscle's force output exactly.

Step 1: Identifying the role of the Agonist.
The agonist (primary mover) is the muscle that contracts to drive a specific joint movement. It does this via concentric contraction, shortening its fibers to pull the skeletal bones closer together. For example, during a bicep curl, the biceps brachii acts concentrically to flex the elbow.

Step 2: Identifying the role of the Antagonist.
The antagonist muscle is located on the opposite side of the joint. During the agonist's movement, the antagonist does not simply turn off. Instead, it undergoes a controlled eccentric contraction, slowly lengthening while maintaining steady tension. This eccentric action acts as a smooth braking mechanism, stabilizing the joint and protecting it from hyperextension or injury. For instance, when lowering your body smoothly into a squat, your quadriceps stretch while contracting eccentrically to control the downward movement against gravity. This behavior matches Option (B).