Heart Rate Zones Explained: What They Are and How to Use Them

Heart rate zones are ranges of heartbeats per minute that correspond to different levels of exercise intensity. They give you an objective way to measure how hard you're working — more reliable than 'feel' alone.

Most training systems use five zones, though some use six or seven. The five-zone model is the most widely used and the easiest to understand:

Zone 1 (50-60% max HR): Recovery — very easy effort. You could hold a full conversation without any breathlessness.

Zone 2 (60-70% max HR): Aerobic base — easy effort. Conversational pace. This is where most of your training should live.

Zone 3 (70-80% max HR): Tempo — moderate effort. You can speak in short sentences but not paragraphs.

Zone 4 (80-90% max HR): Threshold — hard effort. Sustainable for 20-60 minutes. Only a few words at a time.

Zone 5 (90-100% max HR): VO2max — maximum effort. Sustainable for 3-8 minutes. No talking.

Without zones, most athletes train too hard on easy days and too easy on hard days. This 'moderate intensity rut' is the most common training mistake — and it leads to plateaus, fatigue, and overtraining.

Zone-based training ensures you polarize your effort: easy days are genuinely easy (Zone 1-2), and hard days are genuinely hard (Zone 4-5). This polarized approach is backed by decades of research and is how every elite endurance athlete trains.

For triathlon specifically, zones help you pace each discipline. If you start the bike in Zone 4 and your plan says Zone 2-3, you know you're going too hard and will pay for it on the run.

Method 1: Age-based estimate — Subtract your age from 220 to get estimated max HR. Then calculate zones as percentages. This is convenient but can be off by 10-15 bpm for individuals.

Method 2: Max HR field test — Warm up for 15 minutes, then run 3 × 3-minute hill repeats at maximum effort. Your highest heart rate reading is approximately your max HR.

Method 3: Lactate threshold test — Run or ride at maximum sustainable effort for 30 minutes. Average heart rate over the last 20 minutes is your lactate threshold HR (LTHR). This is the most accurate DIY method.

Use our Training Zone Calculator tool to instantly calculate your zones from any of these methods.

Zone 1 — Recovery days and warm-ups: Walk, very easy jog, or easy spin. Use this after hard days and races. It promotes blood flow and recovery without adding stress.

Zone 2 — The foundation: Long runs, long rides, and most swim sessions. This zone builds aerobic capacity, teaches your body to burn fat, and increases mitochondrial density. It should feel embarrassingly easy.

Zone 3 — Use sparingly: Some tempo work belongs here, but don't live in this zone. It's hard enough to fatigue you but not hard enough to trigger significant adaptation.

Zone 4 — Threshold work: Tempo runs, sustained bike efforts, and race-pace swimming. This zone raises your lactate threshold — the speed you can sustain for hours.

Zone 5 — Short intervals only: VO2max intervals of 3-5 minutes with full recovery. Builds peak aerobic power. One session per week is enough for most athletes.

Elite endurance athletes consistently train with approximately 80% of their volume in Zones 1-2 and 20% in Zones 4-5. This is known as polarized training, and research consistently shows it produces better results than threshold-heavy training.

For a beginner training 6 hours per week, this means about 4 hours 45 minutes of easy training and 1 hour 15 minutes of hard training. Most beginners do the opposite — going moderately hard for every session — and wonder why they plateau.

Zone 2 running feels slow. Your friends might pass you. That's fine. You're building the aerobic engine that makes everything else possible.

Chest strap monitors (Polar H10, Garmin HRM-Pro) are the most accurate. They read electrical signals from your heart. Best for structured training and intervals.

Wrist-based monitors (built into most GPS watches) are convenient but less accurate during high-intensity efforts and swimming. Fine for Zone 2 training and general tracking.

Arm-band monitors (Polar Verity Sense, Wahoo TICKR Fit) offer a compromise — more accurate than wrist monitors and more comfortable than chest straps.

For triathlon, a chest strap that pairs with your watch gives you the best data across all three disciplines.