Probably only of interest to runners ...
Last spring I trained for a marathon, so I did several workouts of intervals, once a week beginning with 2 x 1600 m (2 sets of 4 laps, 400 m per lap, with a good break between sets), and building up to 5 x 1600. I didn' keep detailed notes on all the runs, but it seems that when I did 2 sets, the second set was 1:45, 2:00, 1:55 and 1:50; average 1:52. The following week, 3 sets, averaging 1:45, 1:47, 1:48.
Yesterday I did 3 sets, averaging 1:48, 1:46 and 1:50. The first two sets were faster than either of the 2 sets last week. So I'm doing OK, if a bit slower than in the spring. I'm pleased that the second set was faster than the first.
On intervals in the spring, see here and here.