National Academy of Sports Medicine (NASM) Certified Personal Trainer (CPT) Practice Exam

In muscle contractions, what is the primary characteristic of eccentric contractions?

1. Muscle shortening

2. Muscle lengthening

3. Static tension

4. Fast-twitch activation

The correct answer is: Muscle lengthening

Eccentric contractions are characterized by muscle lengthening while under tension. This type of contraction occurs when a muscle generates force but is simultaneously being elongated, usually in response to an external load that exceeds the muscle's force production capability. For example, during the lowering phase of a bicep curl, the bicep muscle is actively contracting while being stretched as the weight is lowered. This is in contrast to concentric contractions where the muscle shortens as it generates force (like lifting the weight), and isometric contractions, where the muscle length remains constant while generating tension (like holding a weight steady without moving). The activation of fast-twitch fibers is more commonly associated with explosive, short-duration activities, but this connection does not specifically define eccentric contractions, which can involve both slow and fast-twitch muscle fibers. Hence, the characteristic of muscle lengthening defines eccentric contractions clearly and accurately.