This week was a big one in my build towards London Marathon 2026—my biggest mileage week ever—and the headline session was a proper 21 mile long run in the Puma Fast-R 3. After testing the Puma Deviate Nitro Elite 4 and deciding it wasn’t going to be my marathon racing shoe of choice, I needed to get serious about longer-distance testing in the Fast‑R 3. So I gave it the job it really needs to handle: a long run where you find out what a shoe feels like when the legs start to fade. Alongside the long run, I take you through the full week of training day-by-day, so you can see how the mileage stacks up and how I’m balancing the sessions as the London build progresses. The big takeaway from this one is simple: short tests don’t tell you enough. If I’m going to trust a shoe on marathon day, it has to prove itself over proper distance, not just a few quicker miles, and this week was all about putting that to the test while keeping the wider training week consistent.