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Running a sub-40:00 10K(r/running)
If you are looking for more structured training, I recommend Pfitzinger’s Faster Road Racing. It covers all the types of training needed for road races between 5k and half marathon, and provides sample training programs.
You may find it much harder to go from 42 to sub 40 than it was from 49 to 42. The difference is bigger than it seems.