Zone 1 - Active Recovery
Very light intensity for recovery days and warm-ups. You should be able to hold a conversation easily.
Zone 2 - Base Training
Aerobic base building. Comfortable pace where you can still talk. Builds endurance and fat-burning capacity.
Zone 3 - Aerobic
Moderate intensity. Conversation becomes more difficult. Improves aerobic capacity and efficiency.
Zone 4 - Lactate Threshold
Hard intensity. Can only speak a few words at a time. Improves lactate threshold and race pace.
Zone 5 - VO2 Max
Very hard intensity. Cannot maintain conversation. Improves maximum oxygen uptake and power.