Variable Time 2 or 3x 4min/3min/2min/1min rests 2m/1:30/1m (5m) 63-70% start 4k PB pace + 12-15 seconds to start. Increase pace at least -3/-4/-5 seconds from the previous rep. You can increase pace by increasing rpm's, increasing DF, or a combination of both. Complete 2 or 3 sets (5min rest between).