Tempo 3x (10:00 cont.) 4:00/3:00/2:00/1:00 rest 3:00-6:00 Each time interval is split 4:00, 3:00, 2:00, 1:00 with a different order every set. Finish where you start! Target 2k/4k PB pace + 16-18 to start, and aim to increase pace on each machine as the times decrease. No rest between machines, but take a 3:00 to 6:00 rest between sets, as needed.