I read yesterday in a runners' book about the importance of running fast the last miles of your long run, to teach the muscles to store more glycogen, because they are pushed to work harder right when they are depleted. Smart!
So today I did 25km, wherein between the 20th and 23rd km I picked up the pace for 3km in 14:40min (ok, not v fast, but better than nothing!) and then the 25th km fast finish (or at least it felt like it). Also, yesterday I did 20km biking.