An important factor in track and field records had been the competition between methods of doping and of doping detection. Endurance records dropped rapidly in the early 1990's with the availability of EPO, but then times increased when tests for first EPO and then CERA were added to antidoping protocols. This seriously confounds first order analysis. If Bolt's time trends are matched by competitors than I would suspect a new doing technique has been discovered which improves explosive power.