How Regulators Drew the Line
The regulatory answer avoided trying to define what a plate may or may not do, because that is a losing battle against material science. Instead it constrained the two things that could be measured objectively. The first is stack height, a limit on how thick the sole may be, with different limits for different disciplines. Since the effect depends on having a deep layer of resilient foam to work with, capping thickness caps the mechanism without needing to describe it. The rules also limit how many rigid plates a shoe may contain, which prevents a shoe from becoming a layered mechanical structure while leaving the single-plate design intact.
The second constraint was availability. A shoe used in competition must be a model that has been on general sale for a period before the event, which ends the practice of racing in a prototype no rival can obtain. This is the part of the response that addressed the actual fairness complaint rather than the technology, and it is arguably the more important half. Governing bodies also began maintaining lists of approved models, which shifts the compliance burden onto manufacturers before a race rather than onto protests afterwards.
