Which muscle action occurs when the muscle lengthens during contraction?

Which muscle action occurs when the muscle lengthens during contraction?

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

Answer: (B)

When a muscle generates force while it is lengthening, that action is called an eccentric contraction. The muscle is activated and resisting the external load, but the fibers get stretched as they contract, controlling or slowing the movement. This occurs a lot in everyday actions like lowering a weight or decelerating the leg after heel strike in running, where the hamstrings or quadriceps lengthen while contracting to manage the motion. In contrast, concentric contractions shorten the muscle as it produces force (like lifting a weight), isometric contractions involve no change in length (holding a position), and isokinetic refers to contractions performed at constant speed, not specifically about length change. So the action described—lengthening under tension—is eccentric.

When a muscle generates force while it is lengthening, that action is called an eccentric contraction. The muscle is activated and resisting the external load, but the fibers get stretched as they contract, controlling or slowing the movement. This occurs a lot in everyday actions like lowering a weight or decelerating the leg after heel strike in running, where the hamstrings or quadriceps lengthen while contracting to manage the motion. In contrast, concentric contractions shorten the muscle as it produces force (like lifting a weight), isometric contractions involve no change in length (holding a position), and isokinetic refers to contractions performed at constant speed, not specifically about length change. So the action described—lengthening under tension—is eccentric.