Im doing a speed workout tomorrow, and am getting bored of doing pretty much the same thing weekly (x amount of 400-1000 meters) so I wanted to do something different. I was going to do 5 sets of different length runs that add up to 1600 meters (my event). For example, I might do
3 x 300, 1 x 700
2 x 800
2 x 600, 1 x 400
1 x 1000, 1 x 600
2 x 600, 2 x 200
I would have equal rest between reps, and a 5 minute break between sets. I wouldn't concentrate on the time of the individual reps, but rather the combined time of the entire 1600. For example, my goal this season is 4:20, so I would try to run between 4:20 and 4:40 for each of the sets, depending upon the length of the reps in the set. Make sense?