Why does Sparta utilize force plates?

At the simplest level, the basis of all movement starts with our interaction with the ground. Because we all live on Earth, we are all bound by the forces of gravity. Our ability to move is best described using physics and the fundamental laws derived by Sir Isaac Newton.

Force

Because of this, the direct measurement of FORCE seems like an obvious place to start, and Force Plates (also called Force Platforms) seems like appropriate tool to use. Our muscles' ability to produce force, even more specifically the complex organization of all of our body systems (neuromuscular, musculoskeletal, sensory, etc) to produce force can ultimately explain all of human movement. 

By standardizing and capturing high-fidelity force data with a large enough population, it becomes possible to analyze and provide insight into not only how well do people produce force (eg how high can I jump, how much weight can I lift, how well can I balance, how well can I sprint), but to the different movement strategies or Movement Signatures that individuals utilize when they move.

When it comes to assessing human movement, force production is fundamental.