Kris Stallenberg 120-min Z2 (Endurance) Medium #09 This is a 'bookend' endurance session with two long, identical blocks of Zone 2 work separated by a short recovery. This structure is mentally manageable and physically effective for building aerobic fitness as described by the Coggan Power Zones. The goal is to maintain a consistent power output in the second block that matches the first, teaching your body to resist fatigue over a long duration. bike