What is the difference between concentric and eccentric muscle contractions?

• A. Eccentric contractions lengthen under tension
• B. Concentric contractions shorten under tension
• C. Both shorten under tension
• D. Both lengthen under tension

Answer: (B)

This question is about how muscles change length when they generate force. Concentric contractions occur when a muscle actively shortens to produce movement—for example, lifting a weight during a bicep curl as the elbow flexes and the biceps shorten. Eccentric contractions happen when a muscle produces force while lengthening to control a movement—such as slowly lowering the weight back down, with the muscle lengthening while still under tension.

The key difference is the direction of length change under load: concentric is shortening, eccentric is lengthening. The statement that concentric contractions shorten under tension correctly describes the action of concentric contractions, making it the best fit. The other options describe eccentric behavior or both shortening/lengthening in a way that doesn’t capture the contrast between the two types. Thinking about lifting versus lowering helps you see why this distinction is the defining one.