Why Heart Rate Matters for Exercise
Your heart rate is a real-time window into how hard your body is working. It's more reliable than "feeling tired" or guessing based on speed. Two people running at the same pace can have completely different heart rates based on fitness level, age, temperature, and stress. Training by heart rate removes the guesswork.
Different heart rate zones burn different fuels and produce different adaptations. Training in zone 2 builds aerobic base and fat burning. Training in zone 4-5 improves VO2 max and speed. Doing everything at zone 3-4 — the most common mistake — leaves you stuck in the middle, building neither endurance nor speed efficiently.
The Five Zones
- Zone 1 (50-60% max HR): Very light. Walking, recovery. Primarily burns fat. Easy enough to have a conversation.
- Zone 2 (60-70% max HR): Light aerobic. Builds base fitness and fat oxidation. Most of your training should happen here.
- Zone 3 (70-80% max HR): Moderate. Aerobic capacity improvement. Sustainable for longer efforts but harder to recover from.
- Zone 4 (80-90% max HR): Hard. Lactate threshold training. You can only sustain this for 20-60 minutes.
- Zone 5 (90-100% max HR): Maximum effort. VO2 max training. Short intervals only.
The Most Common Mistake
Most recreational exercisers spend almost all their cardio time in zone 3 — too hard to recover quickly, too easy to build real fitness. They feel like they're working hard but aren't making the progress they expect.
The fix: do 80% of your cardio in zone 2. Yes, it feels easy. That's the point. Zone 2 training builds the aerobic base that lets you go faster at lower heart rates. Once you have a solid base, add 1-2 zone 4 sessions per week for lactate threshold. You don't need zone 5 unless you're training for very specific speed goals.
Use our heart rate calculator and max heart rate calculator to find your zones.