Kris Stallenberg 45-min Z2 (Endurance) Medium #08 This workout front-loads the effort with the longest Zone 2 interval first, followed by progressively shorter blocks. This 'Descending' structure challenges you to complete the hardest work when you are freshest and then maintain quality as fatigue sets in. It's a great mental and physical test within the Z2 parameters of the Coggan Power Zones, building a resilient aerobic engine. bike