Kris Stallenberg 45-min Z2 (Endurance) Easy #05 This session uses micro-intervals to keep you engaged while staying entirely within your Z2 endurance zone. By alternating between the lower and upper ends of the zone, you'll improve your ability to make subtle power adjustments. This is a great way to build aerobic fitness according to Coggan Power Zones, without the mental fatigue of one long, steady effort. Focus on the smooth transitions between efforts. bike