The last two track seasons I put in 85-90 miles in singles with pretty good results. 8:34-3k and 14:55-5k for outdoors. This track season I have decided to put in more doubles 4 days a week. Most days I will do a 6 and 10 double and on wednesday I do a 10 and 10 double. I am able to handle 100 mile weeks with no problem. With just a increase of 10-15 miles a week with 4 doubles I have already PR'd indoors with a 8:25 and a 14:30. I used to be all about singles but now I am becoming a believer in doubles.