As for whether such an improvement should be regarded with suspicion, fact is, we don’t know. It would be unusual, for Bolt, to make that leap, but not impossible. It would be unusual for ANYONE to make this large an improvement in one month (you can do the comparisons for yourself – you’ll find that is not typical). But there are too many confounding variables to answer that definitively. Ultimately, a big part of it is that an athlete “chooses” how to put their season together, and that obviously influences measured improvements enormously. So, rather than commit to the improvement, I would say that the history of the men’s 100m gives you reason for skepticism of any performance faster than , regardless of how much faster someone gets over X weeks.