Kris Stallenberg 30-min Z2 (Endurance) Medium #01 This workout focuses on a solid, unbroken block of time in your endurance zone. The main 20-minute interval is designed to build aerobic base and improve muscular endurance without accumulating significant fatigue. Based on the Coggan Power Zones, this session targets Z2 (Endurance) to enhance your body's ability to efficiently use fat for fuel. Settle in and focus on a smooth, consistent pedal stroke. bike