I've pored through the new World Athletics regulation that reduces the stack height from 30mm to 25mm for track spikes and what seems very unclear to me is whether this also means if you wear racing flats on the track you're also limited to 25mm. The regulation says 40mm is okay for road events but what about wearing road racing shoes on the track? I realize most elites would never consider flats to begin with but what about masters that are easily injured if wearing spikes?