In early 2024, Max Grüttner, the head of performance concepts at Puma, was examining the results of tests conducted by the company's research and sports science department at its lab in southern Germany. His team was developing a new long-distance "super shoe," the Fast-R Nitro Elite 3, with a newly formulated thermoplastic polyurethane foam and a spoon-shaped carbon fiber plate. The early lab results looked promising -- almost preposterously so.