What are the "zones" that are used in the workouts?

Zone 1
Recovery (< 60%)
Very easy. Promotes blood flow, aids recovery, warm-up/cool-down.

Zone 2
Endurance (61 - 75%)
Easy-steady. Builds aerobic base and fat oxidation; conversational pace.

Zone 3
Tempo (76 - 90%)
Steady-hard. Muscular endurance; sustainable 1–3 hours.

Zone 4
Threshold (91 - 105%)
Hard but controlled. Raises lactate threshold; 8–30 min intervals.

Zone 5
VO2 Max (106 - 120%)
Very hard. Improves max aerobic power; 2–6 min repeats.

Zone 6
Anaerobic (> 121%)
Maximal efforts. Sprints/short bursts; 10 sec to ~2 min.