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Training guide

Maximum heart rate, zones, and the Karvonen method.

Your heart rate is the most accessible real-time window into exercise intensity. Training in the right heart rate zone determines whether you burn fat, build aerobic endurance, push your anaerobic threshold, or drive VO₂ max adaptations and whether you recover well enough to train consistently. All of that starts with knowing your maximum heart rate (MHR).

How to calculate maximum heart rate

Three peer-reviewed formulas dominate practice. All are estimates — individual MHR varies by up to ±10–15 bpm around any age-based prediction, but they're accurate enough for zone training:

The Fox formula (220 − age) is the most widely cited and remains the default in most fitness apps. It overestimates MHR for younger adults and underestimates for older adults. Tanaka corrects this with a meta-analysis of 351 independent studies and is more accurate for adults over 40 and for trained athletes. Gulati was specifically derived from women in a stress-test study and addresses the consistent overprediction of Fox for female subjects, particularly after menopause.

The Karvonen method: personalising your zones

The simple percentage-of-MHR approach ignores a critical variable: how fit you are. Two people the same age can have identical MHRs but very different training capacities if one has a resting HR of 45 bpm (very fit) and the other has 78 bpm (sedentary). The Karvonen method (Heart Rate Reserve method) corrects for this:

Example: Age 35, resting HR 55, Fox MHR 185, targeting Zone 3 (70–80% HRR):

• HRR = 185 − 55 = 130 bpm
• Zone 3 lower = (130 × 0.70) + 55 = 146 bpm
• Zone 3 upper = (130 × 0.80) + 55 = 159 bpm

With simple %MHR (same person): Zone 3 = 130–148 bpm, significantly lower. The Karvonen result is the more accurate training target because it properly accounts for the cardiovascular reserve that a fit person with a low resting HR actually has available.

The five training zones in detail

Zone 1: Very Light (50–60%) · Recovery

Conversational pace. You could sing. Zone 1 promotes active recovery by increasing blood flow without adding metabolic stress. Use it for warm-ups, cool-downs, and on easy days between hard sessions. Elite athletes spend 70–80% of their total training time in Zone 1 and Zone 2 combined, the "polarised training" approach.

Zone 2: Light (60–70%) · Fat Burn

Comfortable effort; you can hold a full conversation. Zone 2 is where fat oxidation peaks as a percentage of fuel use; your aerobic system preferentially burns fat at this intensity because oxygen supply is sufficient for complete fatty acid oxidation. Consistent Zone 2 training builds mitochondrial density, improves insulin sensitivity, and develops the aerobic base that supports all higher-intensity training. Often called the "magic zone" by endurance coaches.

The fat-burning zone myth: while fat is the dominant fuel in Zone 2, total calorie burn is lower than in Zone 4–5. If total fat loss is the goal, higher-intensity training burns more calories per minute (and thus more total fat grams), even though fat is a smaller percentage of the fuel mix.

Zone 3: Moderate (70–80%) · Aerobic Endurance

Comfortably hard. You can speak in short sentences. Zone 3 is the classic "cardio zone"; it improves cardiovascular efficiency, stroke volume (how much blood your heart pumps per beat), and sustained aerobic capacity. Long steady-state runs, bike rides, and swim sets live here. The AHA recommends accumulating at least 150 minutes per week of moderate-intensity exercise (broadly Zone 3).

Zone 4: Hard (80–90%) · Anaerobic / Lactate Threshold

Hard effort; speaking is difficult. Zone 4 is where you cross the lactate threshold. The point at which lactate production outpaces clearance and starts to accumulate. Training here pushes that threshold higher, so you can sustain faster speeds at lower perceived effort over time. Tempo runs, threshold intervals, and cycling time trials are Zone 4 work. This zone produces significant calorie burn and is a primary driver of race performance.

Zone 5: Maximum (90–100%) · VO₂ Max

All-out effort; unsustainable for more than 30–120 seconds. Zone 5 training directly stimulates VO₂ max, the maximum amount of oxygen your body can use per minute, the single strongest predictor of cardiovascular health, longevity, and athletic performance. Short HIIT intervals (20–30 seconds), hill sprints, and track repeats develop this zone. Avoid overuse: Zone 5 requires significant recovery and should represent no more than 5–10% of total training volume.

AHA heart rate recommendations

The American Heart Association recommends a target heart rate of 50–85% of maximum heart rate for aerobic exercise in healthy adults. For a 30-year-old with a Fox MHR of 190 bpm, that's 95–162 bpm, a wide band spanning Zones 1–4. The AHA also recommends:

• 150 minutes/week of moderate-intensity aerobic activity (50–70% MHR, Zones 1–3), or
• 75 minutes/week of vigorous-intensity aerobic activity (70–85% MHR, Zones 3–4), or
• An equivalent combination of both.

How to measure your resting heart rate

Resting heart rate is most accurate when measured immediately after waking, before getting out of bed or drinking coffee:

• Manual method: Place two fingers on your radial pulse (inside wrist, thumb side) or carotid artery (side of neck). Count beats for 60 seconds. Or count for 30 seconds and multiply by 2.
• Wearable average: Most smartwatches measure RHR overnight. A 7-day average is more reliable than a single measurement.

Reference ranges (adults at rest): Athletes: 40–60 bpm; Excellent: 60–65; Good: 65–72; Average: 72–80; Below average: 80–90; Consult a doctor: >100 (tachycardia).

Individual variation and why formulas are estimates

Age-based MHR formulas have a standard deviation of roughly ±10–12 bpm. That means roughly 5% of people will have a true MHR more than 20 bpm away from the formula's prediction. Factors that alter true MHR include genetics, fitness level, altitude acclimatisation, medications (especially beta-blockers which lower MHR), heat and humidity, and daily fatigue. For precision training, a lab VO₂ max test or a supervised maximal exertion field test (under medical supervision) gives a measured MHR.

Disclaimer

Target heart rate zones are estimates for educational and fitness planning purposes. Consult a physician before beginning a new exercise program, especially if you have cardiovascular disease, hypertension, diabetes, or other health conditions. Stop exercise immediately if you experience chest pain, severe shortness of breath, dizziness, or palpitations.