There's a particular type of gym-goer who works absolutely flat out every single session, finishes every cardio workout gasping, and wonders why after six months their fitness hasn't improved as much as they'd hoped. Here's the slightly uncomfortable truth: harder is not always better when it comes to training. Heart rate zones are the framework that explains why — and how to actually get results without destroying yourself every time you lace up your trainers.
What Are Heart Rate Zones?
Heart rate zones are ranges of exercise intensity, defined as percentages of your maximum heart rate (MHR). Training at different intensities causes different physiological adaptations — some build aerobic base, some improve speed, some develop power. The zones help you train with intention rather than just going until you're tired.
There are various zone models (5-zone, 3-zone, 7-zone), but the most common is the 5-zone system:
- Zone 1 (50-60% MHR): Very light — recovery, gentle walking
- Zone 2 (60-70% MHR): Light — fat burning, building aerobic base
- Zone 3 (70-80% MHR): Moderate — improving aerobic efficiency
- Zone 4 (80-90% MHR): Hard — lactate threshold, speed work
- Zone 5 (90-100% MHR): Maximum — all-out sprinting, anaerobic power
Calculating Your Maximum Heart Rate
The classic formula is simply 220 − your age. A 35-year-old would have an estimated MHR of 185 beats per minute (bpm). This formula is a population average — individual MHRs can vary by 10-20 bpm from this estimate. For general training purposes it's fine; for competitive athletes, a lab test or field test gives a more accurate figure.
Use our fitness goal calculator to apply your MHR to your specific training objectives.
Zone 2: The Most Underrated Zone
Zone 2 training has become something of a hot topic among endurance athletes, longevity researchers, and coaches. At 60-70% MHR (for most people, a pace where you can hold a full conversation without gasping), you're training your aerobic energy system to become more efficient — increasing the density of mitochondria (the energy-producing organelles in cells), improving fat oxidation, and building the aerobic base on which all higher-intensity training depends.
Most recreational exercisers do too little Zone 2 work. The counterintuitive truth is that spending 70-80% of your training time in Zone 2 and only 20-30% in harder zones leads to better results than grinding away at Zone 3-4 most of the time.
Zone 4: Threshold Training
Your lactate threshold is the intensity at which lactate starts accumulating in the blood faster than it can be cleared — the point where the burning sensation in your muscles begins. Training at or slightly below this threshold (Zone 4) raises it over time, allowing you to sustain higher speeds with the same effort. This is where race pace work, tempo runs, and cycling time trial efforts typically sit.
Zone 4 is hard work. It should be reserved for specific sessions, not every workout. Our calories burned calculator can help you estimate energy expenditure at different training intensities.
Zone 5: The Short Sharp Shock
True Zone 5 training — at 90%+ of MHR — is very hard and can only be sustained for short intervals. High-intensity interval training (HIIT) often dips into Zone 5. The adaptations include improved VO2 max (maximum oxygen uptake), power output, and neuromuscular recruitment. It's effective but needs to be balanced with sufficient recovery time.
How to Monitor Your Heart Rate During Training
Options range from budget to sophisticated:
- Chest strap monitors: most accurate, picks up heart rate via electrical signal
- Wrist-based optical monitors: convenient (built into most fitness watches), but less accurate — particularly during high-intensity efforts
- Perceived exertion: the low-tech option — a 1-10 scale of how hard you feel you're working correlates reasonably with heart rate zones
A Simple Weekly Structure Using Heart Rate Zones
- 2-3 sessions per week in Zone 2 (easy, conversational pace)
- 1 session in Zone 3-4 (tempo/threshold work)
- Optionally 1 short HIIT session in Zone 4-5
- Remaining days: rest or active recovery (Zone 1)
This 80/20 structure (80% easy, 20% hard) is what most elite endurance coaches recommend and what research supports for long-term fitness development. It's also far more sustainable than going hard every session — and leads to far fewer injuries.
Further reading: The British Heart Foundation has excellent resources on exercise intensity and heart health. Read the British Heart Foundation's guide to exercise intensity.