Kris Stallenberg 45-min Z4 (Threshold) Medium #10 This mixed-block session combines a long, steady-state threshold effort with short, high-intensity repeats. The initial 15-minute block builds your endurance, while the final set of 2-minute intervals sharpens your top-end power. This combination creates a versatile workout that improves both your sustained power and your ability to accelerate when fatigued. bike