Final answer:
During the concentric phase of plyometric exercise, rapid muscle shortening occurs, which is a type of isotonic contraction involving the muscle shortening to move a load. Therefore, the correct option is B.
Step-by-step explanation:
The type of movement that happens during the concentric phase of plyometric exercise is rapid muscle shortening. This phase of the exercise is associated with isotonic contractions where the muscle shortens to move a load. For instance, the biceps brachii muscle during a bicep curl shortens as the hand weight is brought upward, decreasing the angle of the elbow joint. This contraction is characterized by the sarcomeres in the muscle fibers shortening and the myosin heads pulling the actin to move the weight, which is the concentric phase.