Interval interval sessions mix short, fast efforts with planned recovery to boost your aerobic and anaerobic systems and raise race pace. You’ll target 85–95% max heart rate or 10–20 seconds faster than goal pace, use 30s–2min work with equal or longer recovery, and favor active recovery for lactic clearance. Warm up thoroughly, monitor RPE and heart rate, fix form faults, and avoid consecutive hard days; continue for progressive protocols and specific workouts to learn more.