Which muscle action produces tension while shortening to overcome external resistance?

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

Answer: (D)

Concentric contractions occur when a muscle produces tension and shortens as it overcomes external resistance to create movement. This is the action that actually drives a move, like during a bicep curl when the biceps shorten to lift the weight toward the shoulder. In contrast, isometric contractions generate force without changing the muscle's length (no movement); eccentric contractions involve the muscle lengthening while still under tension as it controls lowering a load; a synergist is simply a muscle that assists the primary mover, not a description of the contraction length change. So the action described—tension plus shortening to move against resistance—fits concentric contraction.