Heart rate zones are ranges of exercise intensity, set as percentages of your maximum heart rate, and each one drives different changes in your body. If every run or ride ends up at the same moderate effort, progress tends to stall. Spreading your training across the right zones is what keeps athletes improving year after year, and it starts with knowing what each zone does and where your own zones sit.
What Are Heart Rate Training Zones?
The zones split everything between complete rest and maximum effort into bands. Each band is a different metabolic state, with its own fuel mix, muscular demands, cardiovascular stress, and adaptation signal. Effort is hard to judge by feel (what feels "moderate" today will feel easy in six months), so heart rate gives you an objective, real-time measure.
The most widely used system in endurance sports is a five-zone model. It starts from the two lactate thresholds, which split intensity into three metabolic regimes, and subdivides those for practical training.
The Five Heart Rate Zones: Definitions and Physiology
Zone 1 — Warmup (50–59% 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. Think of Zone 1 as recovery. 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 — Fitness (60–69% 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 blood lactate first starts to rise above resting levels. The main adaptations are 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 do around 80% of their sessions in Zones 1 and 2, and often more of their total training time. Many coaches recommend building toward 3–4 or more hours of Zone 2 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 — Endurance (70–79% 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: Run with a faster friend and you may settle at a pace where you'd rather talk in short phrases than full sentences. That's Zone 3: comfortably hard, with breathing clearly elevated and demanding some attention.
Zone 4 — Hardcore (80–89% 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. Holding it takes focus.
Zone 5 — Red Line (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
Your zones are only as accurate as your max heart rate. Use the most precise method available to you, then plug it into our heart rate zone calculator to get your zones in bpm.
220 Minus Age (Simple Estimate)
The most commonly cited formula. A 35-year-old's predicted max HR = 185 bpm. Simple and familiar, but it has a standard deviation of ±10–12 bpm, so your 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. 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)
Warm up with a moderate workout, build your effort over the final few minutes, finish with a 1-minute all-out effort, 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, as hard as you can go
- 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) follow a similar pattern: roughly 80% of sessions below the first lactate threshold (Zones 1–2) and 20% at or above the second lactate threshold (Zones 4–5), with relatively little time in the middle. Measured by time rather than sessions, the easy share is often even higher, because hard sessions include easy warm-ups and cool-downs.
Several training studies have found this distribution works as well as or better than programs concentrated in the "moderate" middle zone (Stöggl and Sperlich, 2014). The usual explanation: too much Zone 3 adds fatigue that can compromise the quality of your hard sessions, without adding much benefit beyond what easy training already provides. Because Zone 2 costs so little fatigue, the 80/20 model lets you train at high volume and still come into your hard sessions recovered enough to do them well.
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
Treat these numbers as a guideline. With under 5 hours per week, more Zone 3 training may be appropriate; the model pays off most at 6+ hours per week.
To check your own split in FITIV Pulse, tap the Heart Rate Zones card on the Today tab and pick a range from 7d to 2y; the totals show your time in each zone. Under Zones Included, select just Zones 1 and 2 to see your easy time on its own.
How to Set Up Heart Rate Zones in FITIV Pulse
Setting up your zones in FITIV takes about two minutes, and every workout after that uses them.
Set your max and zone method
- Open the More tab and tap Heart Rate
- Tap Maximum Heart Rate and pick a formula (Tanaka, Monahan, & Seals, the default, Haskell & Fox, or Nes, et al.), or choose Manual to enter a max from a test
- Choose your Training Method: Percent of Maximum Heart Rate (the default), Percent of Heart Rate Reserve, which also uses your Resting Heart Rate, or Percent of Lactate Threshold Heart Rate
- FITIV calculates all five zones from these settings and lists them on the same screen
If you leave the default formula in place, FITIV uses the Tanaka formula (208 – 0.7 × age) with your date of birth, so your zones are calculated automatically and updated on each birthday.
During any workout with heart rate, FITIV shows your current zone live. To hear when you cross a boundary, set the Heart Rate Zone trigger in Voice Coaching to On Change; on Apple Watch, Heart Rate Zone Change Haptics taps your wrist instead. Either one helps you hold a Zone 2 ceiling or stay in Zone 4 during threshold intervals.
Afterward, every workout summary includes a time-in-zone breakdown showing minutes and percentage spent in each of the five zones. It's the clearest check on whether your training distribution matches your program goals. To see zone time across all your sessions, tap the Heart Rate Zones card on the Today tab.
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 | Z1 | 30–45 min |
| Tuesday | Zone 2 run or bike | Z2 | 60 min |
| Wednesday | Threshold intervals | Z4 | 60 min (incl. warm-up) |
| Thursday | Zone 2 | Z2 | 75 min |
| Friday | Rest or Zone 1 | Z1 | 30 min |
| Saturday | VO2 max intervals | Z5 | 55 min (incl. warm-up) |
| Sunday | Long Zone 2 | Z2 | 90 min |
Two of the seven sessions are hard, so by session count this week is about 70/30. By time it lands at roughly 80/20 or more: the five easy days alone add up to about 5 of the week's 7 hours, and much of each hard session is easy warm-up, recovery, and cool-down.
Frequently Asked Questions
What is the difference between heart rate zones and power zones for cyclists?
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.
Is a 3-zone or 5-zone model better?
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.
My heart rate is always too high in Zone 2 — what am I doing wrong?
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 base is less developed than your ability to push hard, so an easy heart rate feels slow at first. 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.
Do heart rate zones change as I get fitter?
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.
Why do some apps show 6 or 7 zones instead of 5?
Zone models vary by source. Garmin and Polar use 5-zone models. Some plans use Coggan's 7-zone power model adapted to HR. Much of the research literature uses a 3-zone model built around two lactate or ventilatory 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.
