Kris Stallenberg 90-min Z4 (Threshold) Pushing #01 This classic threshold workout builds your ability to sustain power for long durations. By completing three extended intervals at your functional threshold power (FTP), you'll improve lactate clearance, increase metabolic efficiency, and build immense mental toughness. This session is a cornerstone for time trialists, climbers, and any rider looking to raise their sustainable power output. bike