Tempo 4x (9:00 cont.) 4:30/3:00/1:30* rest 3:00-6:00 Each time interval is split equally between the machines (1:30, 1:00, and 0:30 on each). 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.