Final answer:
Clients should always use athletic shoes when performing plyometric training to provide necessary support and cushioning, reducing the risk of injury due to the exercises' high-impact nature.
Step-by-step explanation:
The exercise equipment that clients should always use when performing plyometric training, due to its high-impact nature, is D. Athletic shoes. Plyometric exercises involve explosive movements such as jumping, hopping, and bounding, which can place a significant amount of stress on the feet, ankles, knees, and legs. Quality athletic shoes provide the necessary support, cushioning, and stability to absorb the impact and reduce the risk of injury. These considerations are paramount for a safe plyometric workout. It's important to choose shoes that are appropriate for the type of plyometric activity and the surface on which it will be performed.