During concentric contraction, what happens to muscle length?

• A. The muscle length increases
• B. The muscle length decreases
• C. The muscle length remains the same
• D. The muscle length fluctuates unpredictably

Answer: (B)

Concentric contraction is when a muscle shortens as it contracts to move a load. The myosin heads pull actin filaments toward the center of the sarcomere, shortening the sarcomeres and thus reducing the overall muscle length. An example is curling a dumbbell—the biceps shorten as the elbow flexes to lift the weight. The length decreases during concentric contraction; it would lengthen during eccentric contraction or stay the same during an isometric contraction.