Differentiate concentric from eccentric contraction with an example.

• A. Concentric: lengthens while producing force; eccentric: shortens.
• B. Concentric: shortens; eccentric: lengthens.
• C. Concentric: produces no movement; eccentric: produces movement.
• D. Concentric: only occurs with fast movements; eccentric only slow.

Answer: (B)

Focus on how muscle length changes during contraction. Concentric contractions shorten the muscle as it generates force, producing movement. Eccentric contractions lengthen the muscle while it still produces force, acting to control or resist a load.

For example, when you curl a dumbbell toward your shoulder, the biceps shorten—that’s concentric. As you slowly lower the dumbbell back down, the biceps lengthen while still contracting to control the motion—that’s eccentric.

The other descriptions mix up length change or movement: a statement claiming concentric lengthens is incorrect, as is one saying concentric produces no movement; and tying these contractions to speed alone doesn’t capture the basic difference.