Final answer:
If not all stored elastic energy from the eccentric phase is used during the concentric phase of a plyometric exercise, it results in reduced force production.
Step-by-step explanation:
If the concentric phase of a plyometric exercise doesn't use all the stored elastic energy from the eccentric phase, the result is b. Reduced force production.
This is because the elastic energy that was stored in the muscles during the eccentric phase—where muscles lengthen under tension—is not fully utilized during the subsequent concentric contraction, where muscles shorten. When this energy is not fully employed, the muscles cannot produce the maximum amount of force.