Kris Stallenberg 90-min Z2 (Endurance) Medium #04 This workout builds a strong endurance base while incorporating short 'surges' into the Tempo zone (Zone 3). These brief increases in effort, followed by an immediate return to Zone 2, help improve your aerobic efficiency and ability to recover from harder efforts while still riding. The majority of this ride is based on the Coggan Power Zones' Level 2, ensuring a strong aerobic stimulus. bike