Kris Stallenberg 30-min Z2 (Endurance) Easy #04 This session is a progressive endurance ride. Each block gently increases the intensity, moving you through the full range of your Z2 (Endurance) zone. According to the Coggan Power Zones, this type of sustained, progressive effort is excellent for building a strong aerobic foundation and improving your ability to sustain power over time. Pay attention to how your body feels as the effort slowly rises. bike