Kris Stallenberg 60-min Z2 (Endurance) Easy #08 This workout, known as 'micro-bursts' or 'over-unders,' keeps you entirely within Zone 2 but constantly varies the intensity. These small fluctuations between the lower and upper end of the zone improve your ability to control power output and adapt to subtle changes in terrain or pace. It's an engaging way to train within the Coggan Power Zones for endurance. bike