Which statement correctly describes concentric, eccentric, and isometric muscle actions?

• A. Concentric: shortening under load; Eccentric: lengthening under load; Isometric: tension without length change
• B. Concentric: lengthening under load; Eccentric: shortening under load; Isometric: movement with length change
• C. Concentric: shortening under load; Eccentric: lengthening under load; Isometric: tension without length change
• D. Concentric: shortening under load; Eccentric: shortening under load; Isometric: tension with length change

Answer: (C)

Concentric, eccentric, and isometric actions describe how a muscle changes length while producing force.

During concentric action, the muscle shortens as it generates force against resistance—think lifting a weight where the elbow flexes and the biceps pull the forearm upward.

During eccentric action, the muscle lengthens while still producing force as it controls the movement against load—such as slowly lowering the weight and the muscle resisting the stretch.

During isometric action, the muscle tenses and produces force but does not change length—the joint angle stays the same, as in holding a weight steady without moving.

So the correct description is: concentric shortening under load, eccentric lengthening under load, and isometric tension without length change. For context, the lifting phase is typically concentric, the lowering phase eccentric, and a static hold is isometric.