Which is NOT one of the three most commonly found muscular contractions?

• A. Concentric
• B. Isometric
• C. Eccentric
• D. Plyometric

Answer: (D)

Muscle actions are categorized by how the muscle length changes while it’s producing force: concentric contractions shorten the muscle, eccentric contractions lengthen it under load, and isometric contractions generate force without changing length. These three are the basic, most commonly described muscle actions you’ll see in movement analysis and training programming. Plyometric, on the other hand, is not a contraction type. It’s a training method that uses a rapid stretch (eccentric) followed by an explosive shortening (concentric) to develop power, leveraging the stretch-shortening cycle. Because it’s a method rather than a standalone contraction type, it doesn’t belong in the list of the three basic muscle actions. So the correct choice is plyometric.