Why Training Zones Matter
Different heart rate intensities develop different physiological systems. Training always at the same moderate intensity is one of the most common endurance training mistakes, it's too hard to build aerobic base but too easy to develop speed or VO2max.
Structuring training across zones produces far better results than undifferentiated effort.
The 5 Zones
| Zone | % Max HR | Feel | Benefit |
|---|---|---|---|
| Z1, Recovery | 50-60% | Very easy, fully conversational | Active recovery, fat burning |
| Z2, Aerobic | 60-70% | Easy, can hold conversation | Aerobic base, mitochondrial density |
| Z3, Tempo | 70-80% | Moderate, breathing harder | Aerobic efficiency |
| Z4, Threshold | 80-90% | Hard, few words at a time | Lactate threshold, race speed |
| Z5, VO2 Max | 90-100% | Maximum effort | VO2max, speed, power |
Zone 2, The Most Important Zone
Zone 2 is arguably the most important zone for endurance athletes. It specifically develops mitochondrial density and fat oxidation capacity, the aerobic foundation that supports all higher-intensity work. Most recreational athletes significantly underdevelop Zone 2 by running too hard on easy days.
If you can't hold a comfortable conversation, you're probably not in Zone 2. Slowing down on easy days is one of the most impactful changes most people can make.
The 80/20 Distribution
Research on elite endurance athletes shows approximately 80% of training time in Zones 1-2 and only 20% at Zone 3 and above. This polarised approach builds a large aerobic base while allowing sufficient high-intensity work to improve speed. It's the opposite of what most recreational athletes do.
