Heart Rate Zones Explained: Training in Zones 1–5
Heart rate zones are ranges of exercise intensity defined as percentages of your maximum heart rate, each associated with distinct physiological processes and training adaptations. Training systematically across the right zones — rather than defaulting to the same moderate effort every day — is what separates athletes who stall from athletes who make consistent year-over-year progress. This guide explains all five zones, what each one does to your body, how to calculate your zones accurately, and how to apply them in a coherent training program.
What Are Heart Rate Training Zones?
Heart rate zones divide the intensity spectrum between complete rest and maximum effort into meaningful bands. Each zone represents a different metabolic state: different fuel sources, different muscular demands, different cardiovascular stresses, and different adaptation signals. Because exercise intensity cannot be neatly felt or guessed — what feels "moderate" today will feel easy in six months — heart rate provides an objective, real-time intensity measure.
The most widely used system in endurance sports is a five-zone model, derived from the two lactate thresholds that divide the exercise intensity spectrum into three metabolic regimes, then subdivided for practical training purposes.
The Five Heart Rate Zones: Definitions and Physiology
Zone 1 — Active Recovery (50–60% of Max HR)
Physiological purpose: Promotes blood flow and metabolic waste clearance without generating meaningful training stress. At Zone 1, the body is working below the first lactate threshold and is fueled almost entirely by fat oxidation. Lactate produced is minimal and is cleared almost as fast as it is generated.
When to use it: Recovery days, warm-up and cool-down phases, between interval repetitions. Zone 1 is not a "training zone" in the adaptation sense — it is a recovery modality. Professional cyclists use Zone 1 on rest days to promote blood flow without adding fatigue.
How it feels: Effortless. You could hold a detailed conversation, read, or sing without any increase in breathing effort. Walking at a comfortable pace for most people.
Zone 2 — Aerobic Base (60–70% of Max HR)
Physiological purpose: The most important zone for endurance base building. Zone 2 intensity is just below the first lactate threshold — the point at which lactate begins accumulating faster than it can be cleared. The primary adaptation is mitochondrial biogenesis (growth of energy-producing organelles in muscle cells), improved fat oxidation capacity, increased capillary density, and enhanced cardiac stroke volume.
When to use it: The foundation of any endurance program. Elite endurance athletes spend 70–80% of total training volume in Zones 1 and 2. Minimum effective Zone 2 dose for adaptation: 3–4 hours per week.
How it feels: Conversational — you can speak full sentences without gasping, but breathing is noticeably elevated. Roughly the pace where you could comfortably hold a podcast conversation on a run.
Zone 3 — Aerobic Threshold / Tempo (70–80% of Max HR)
Physiological purpose: Zone 3 lies between the first and second lactate thresholds — the "moderate intensity trap" that many recreational athletes live in. It is intense enough to accumulate significant fatigue yet not intense enough to produce the mitochondrial stimulus of Zone 2 or the cardiac and neuromuscular stimulus of Zones 4–5. Zone 3 provides some threshold development and aerobic conditioning but is the least efficient use of training time in a polarized program.
When to use it: Moderate tempo runs, aerobic threshold work, "comfortably hard" steady-state sessions. Has utility in building programs or when total training time is very limited.
How it feels: Comfortably hard. Sentences are possible but uncomfortable — you prefer to speak in short phrases. Breathing is clearly elevated and demands some attention.
Zone 4 — Lactate Threshold / Sub-threshold (80–90% of Max HR)
Physiological purpose: Zone 4 trains at or near the second lactate threshold — the highest intensity at which lactate production and clearance remain roughly balanced. Sustained Zone 4 work raises the lactate threshold, meaning you can maintain faster absolute speeds or higher power outputs before lactate accumulates. This is the zone where cycling threshold (FTP) training, running tempo work, and 10K–half marathon race pace occur.
When to use it: Threshold intervals (20–40 minute tempo efforts, cruise intervals), sub-threshold long intervals. 1–2 sessions per week in a structured program.
How it feels: Hard but sustainable. Conversation is reduced to single words between breaths. This is a demanding intensity that requires focus to maintain.
Zone 5 — VO2 Max / Neuromuscular (90–100% of Max HR)
Physiological purpose: Zone 5 encompasses the intensities close to and at VO2 max. At these intensities, cardiac output is maximized, and the primary training adaptation is increased stroke volume and maximum cardiac output — the physiological basis of VO2 max itself. Zone 5 also includes all-out sprint work that trains neuromuscular power and anaerobic capacity.
When to use it: VO2 max intervals (4x4 minutes, 6x3 minutes), short high-intensity intervals, race-pace work at 5K intensity. 1–2 sessions per week maximum; more leads to overreaching.
How it feels: Very hard to maximal. Conversation is impossible. Breathing is labored. Effort is clearly unsustainable for more than minutes.
How to Calculate Your Maximum Heart Rate
The accuracy of all five zones depends entirely on the accuracy of your maximum heart rate estimate. Use the most precise method available to you.
220 Minus Age (Simple Estimate)
The most commonly cited formula. A 35-year-old's predicted max HR = 185 bpm. Simple and familiar, but statistically has a standard deviation of ±10–12 bpm — meaning actual max HR can easily be 10–15 bpm above or below the prediction.
Best for: Beginners with no testing experience who need a starting point.
Tanaka Formula: 208 – (0.7 × Age)
A more accurate regression developed from a meta-analysis of 351 studies involving over 18,000 subjects. A 45-year-old: 208 – (0.7 × 45) = 208 – 31.5 = 176.5 bpm. More precise than 220-age, particularly for athletes over 40.
Best for: Athletes who cannot perform a max test but want more accuracy than the simple formula.
Field Test (Most Practical for Self-Testing)
Run or cycle to near-exhaustion at the end of a hard workout, perform a 1-minute all-out sprint at the end, and note the highest HR observed. This is your observed max HR and is far more accurate than any formula. Perform the test on a day when you are well-rested and healthy.
Protocol:
- Complete a normal workout of moderate intensity (45 minutes)
- In the final 5 minutes, push progressively harder
- Final 60 seconds: maximum effort — go as hard as you can
- Note the peak HR reading
Best for: Athletes with basic fitness and a heart rate monitor.
Laboratory VO2 Max Test
A graded exercise test with progressive intensity increments under laboratory supervision. The most accurate possible maximum HR measurement. Also provides lactate threshold data for precise zone setting.
Best for: Serious athletes, those with cardiac concerns, professional programs.
The Polarized Training Model: 80/20 Distribution
Decades of sport science research, most notably from exercise physiologist Stephen Seiler, have consistently found that elite endurance athletes — across running, cycling, rowing, cross-country skiing, and swimming — distribute their training time in a highly polarized pattern: approximately 80% below the first lactate threshold (Zones 1–2) and 20% above the second lactate threshold (Zones 4–5). Zone 3 — the middle — is largely avoided.
This distribution produces superior adaptations to training programs that concentrate in the "moderate" middle zone. The mechanism is understood: Zone 3 is fatiguing enough to compromise the quality of high-intensity sessions while not being aerobically stimulating enough to provide Zone 2's mitochondrial benefits. The 80/20 model allows high training volume (enabled by the low fatigue cost of Zone 2) while maintaining the quality of high-intensity sessions (because athletes are adequately recovered).
For recreational athletes training 6–8 hours per week:
- 4.5–5.5 hours in Zones 1–2
- 1–1.5 hours in Zones 4–5
- Minimal Zone 3
This is a principle, not a rigid prescription. Athletes with time constraints under 5 hours per week may find more Zone 3 training appropriate. The model is most beneficial for athletes with 6+ hours per week.
How to Set Up Heart Rate Zones in Fitiv Pulse
Setting up accurate zones in Fitiv takes about two minutes and improves the precision of every subsequent workout.
Method 1: Maximum HR entry
- Navigate to Profile > Training Zones
- Enter your maximum heart rate (from a test or formula)
- Fitiv automatically calculates all five zones as percentages of your max HR
Method 2: Date of birth automatic calculation Fitiv uses the Tanaka formula (208 – 0.7 × age) if you have entered your date of birth. Zones are calculated automatically and updated on each birthday.
Zone display during workouts: All workout types in Fitiv (running, cycling, rowing, elliptical, strength) display a real-time heart rate gauge with colored zone bands. The current zone is highlighted, and configurable audio alerts notify you when you cross zone boundaries — useful for maintaining Zone 2 ceiling discipline or staying in Zone 4 during threshold intervals.
Time in Zone reports: Every workout summary includes a time-in-zone breakdown showing minutes and percentage spent in each of the five zones. This is the primary tool for assessing whether your training distribution matches your program goals. The weekly training dashboard aggregates zone distributions across all sessions.
Applying Zone Training: A Practical Weekly Structure
For an athlete training 7 hours per week following a polarized model:
| Day | Session | Zone Target | Duration | |-----|---------|-------------|----------| | Monday | Rest or Zone 1 walk | Zone 1 | 30–45 min | | Tuesday | Zone 2 run or bike | Zone 2 | 60 min | | Wednesday | Threshold intervals | Zone 4 | 60 min (incl. warm-up) | | Thursday | Zone 2 | Zone 2 | 75 min | | Friday | Rest or Zone 1 | Zone 1 | 30 min | | Saturday | VO2 max intervals | Zone 5 | 55 min (incl. warm-up) | | Sunday | Long Zone 2 | Zone 2 | 90 min |
Zone 2 total: ~4.5 hours. Zones 4–5 total: ~1.5 hours. Approximate 75/25 distribution.
Frequently Asked Questions
Q: What is the difference between heart rate zones and power zones for cyclists? A: Heart rate zones are defined as percentages of max HR; power zones are defined as percentages of FTP (Functional Threshold Power). They describe different aspects of exercise intensity. Power responds instantly to effort changes; heart rate lags 30–60 seconds. For steady-state work, both methods target similar metabolic states. For interval training, power-based zones are preferred because they respond to every pedal stroke. For events where power meters are unavailable (running, swimming, rowing), HR zones are the primary tool. Fitiv supports both HR and power zones for cycling.
Q: Is a 3-zone or 5-zone model better? A: Both have merit. Elite programs and sport science research often use a 3-zone model (below first threshold, between thresholds, above second threshold) for analysis. The 5-zone model provides more granularity that is useful for practical training. Fitiv uses the 5-zone model because it gives athletes more precise guidance during workouts — the distinction between Zone 2 (aerobic base) and Zone 3 (moderate) matters for program design, even if Zone 2 and Zone 3 share some physiological characteristics.
Q: My heart rate is always too high in Zone 2 — what am I doing wrong? A: You are probably not doing anything wrong. Most athletes new to zone-based training find that their Zone 2 pace is significantly slower than their usual training pace. This is because your aerobic system is less developed than your cardiovascular system. Slow down until the heart rate drops to the Zone 2 target. Over months of consistent Zone 2 training, your pace at the same heart rate will increase substantially.
Q: Do heart rate zones change as I get fitter? A: Zone boundaries change only if your maximum heart rate changes (uncommon) or if you retest your max HR. However, your performance within the zones changes dramatically with fitness — as you get fitter, you can sustain faster paces and higher power outputs at the same heart rate. Update your zones in Fitiv after any max HR retest or at least annually.
Q: Why do some apps show 6 or 7 zones instead of 5? A: Zone models vary by source. Garmin and Polar use 5-zone models. Some plans use Coggan's 7-zone power model adapted to HR. The Norwegian system uses 3 zones based on lactate thresholds. The underlying physiology is the same — the zone count is a labeling convention. Fitiv's 5-zone model aligns with the most widely used standard in sport science and coaching literature.