Zone 1 is mainly based on recovery, but we won’t actually run in this zone. This is mainly of interest for other workouts (e.g. cycling).
Zone 2, also called the LSD zone (Long Slow Distance) is especially interesting for improving your basic fitness. We will train in this zone almost 80% of the time. I know that, especially in the beginning, it is very frustrating to run in this zone, but the better you stick to this low heart rate in the beginning, the faster you will start noticing progression as well.
Zone 3, I often call this zone the ‘intermediate zone’. You will notice that in this zone you start to run a bit ‘smoother’, but to maintain this pace for a very long time is not easy either. This zone is used to ease the transition to zone 4.
Zone 4, is around your ‘threshold pace’. In other words, your tipping point. If you start running in this zone for a long time, your body will start producing lactate. This in itself is not bad, but this is definitely unpleasant. This zone is mainly used for intervals and to improve your max speed.
Zone 5, this zone is really your ‘max’ zone. Running in this zone cannot be sustained for long because of the lactic acid that will accumulate in your muscles and cause cramping. Running in this zone is mainly by character.