Kris Stallenberg 45-min Z2 (Endurance) Easy #09 This session uses progressively longer intervals within the Z2 range to build your endurance and mental fortitude. As the intervals extend, your body adapts to holding a steady aerobic effort for longer durations. According to Coggan Power Zones, this type of training is key for developing a strong aerobic engine. The short recoveries allow just enough time to reset before the next block. bike