How to make your 200m time faster

With the World Indoor Athletics Championships underway, I thought it would be good to look at some of the Men’s 200m outdoor times.

Have a look at the graph below that Paula Jardine has collated. 

If you look at Carl Lewis, he appears to have a steady progression and consistent set of results.  Michael Johnson has some very sharp peaks, indicating a rapid increase in performance in a short time.

What could possibly lead to such sudden improvements in running time, for someone who is already a fast runner?

Any thoughts are welcome in the comments below.