Kris Stallenberg 60-min Z2 (Endurance) Pushing #02 Challenge your aerobic system with Z2 over/unders. This session oscillates between the high and low ends of your endurance zone, forcing your body to adapt to subtle changes in intensity without leaving the Z2 (Endurance) range. This structure, based on Coggan Power Zones, enhances metabolic flexibility and builds resilience for rides with variable pacing. bike