Heart-rate zones for training.
THR = (HRR × I) + RHR where HRR = MHR − RHR and MHR = 208 − (0.7 × Age)
The Karvonen formula calculates target heart rate by factoring in your heart rate reserve (HRR) — the difference between your maximum heart rate and your resting heart rate. This produces a more personalized result than simply using a percentage of maximum heart rate alone.
Step 1 – Estimate Maximum Heart Rate (MHR): The most widely used estimate is the Tanaka formula (more accurate than the older 220 − age method):
MHR = 208 − (0.7 × Age)
Step 2 – Calculate Heart Rate Reserve (HRR):
HRR = MHR − RHR
Step 3 – Calculate Target Heart Rate at a given intensity (%):
THR = (HRR × Intensity%) + RHR
Typical intensity ranges: 50–60% (light/fat-burning), 60–70% (aerobic base), 70–80% (aerobic endurance), 80–90% (threshold/anaerobic), 90–100% (peak/VO₂ max).
Step 1 — Maximum Heart Rate: MHR = 208 − (0.7 × 35) = 208 − 24.5 = 183.5 ≈ 184 bpm Step 2 — Heart Rate Reserve: HRR = 184 − 62 = 122 bpm Step 3 — Target Heart Rate at 70%: THR = (122 × 0.70) + 62 = 85.4 + 62 = 147.4 ≈ 147 bpm
Result: **Target Heart Rate ≈ 147 bpm** at 70% intensity. Full aerobic zone (60–80%): approximately **135–160 bpm** for this individual.
A result of 147 bpm means that during aerobic endurance training, this 35-year-old should aim to keep their heart rate close to 147 beats per minute. Working at this intensity improves cardiovascular efficiency and endurance without pushing into the anaerobic threshold zone. If the goal were fat-burning (60–70%), the range would be roughly 135–147 bpm; for threshold training (80–90%), it would be approximately 160–172 bpm. Always monitor how you feel — perceived exertion and breathing difficulty are equally important signals.
Training zones divide the spectrum between rest and maximum effort into bands, each eliciting different physiological adaptations:
| Zone | Intensity | Benefit | |---|---|---| | Zone 1 – Light | 50–60% | Recovery, general health | | Zone 2 – Fat Burning | 60–70% | Fat oxidation, aerobic base | | Zone 3 – Aerobic | 70–80% | Cardiovascular endurance | | Zone 4 – Threshold | 80–90% | Lactate threshold, speed | | Zone 5 – Peak | 90–100% | VO₂ max, anaerobic capacity |
A simple percentage of maximum heart rate (e.g., "train at 70% of 184 bpm = 129 bpm") ignores your resting heart rate entirely. The Karvonen method corrects for this by using Heart Rate Reserve, which personalizes the calculation to your actual cardiovascular fitness level. A well-trained athlete with an RHR of 45 bpm and a sedentary person with an RHR of 80 bpm have very different working ranges even at the same age.
For the most accurate THR calculation, measure RHR on 3 consecutive mornings immediately upon waking (before standing or checking your phone) and average the results. A single measurement may be elevated by poor sleep, stress, or caffeine.
At high altitude, the reduced oxygen availability causes your heart to beat faster at any given workload to compensate. This means your effective heart rate zones shift — what felt like Zone 2 effort at sea level may push you into Zone 3 at 8,000 feet. It is advisable to train by perceived exertion (RPE) rather than strict bpm targets when exercising at altitude until your body acclimatizes, typically over 1–2 weeks.
Yes, but with modifications. During high-intensity intervals, you are targeting **Zone 4–5 (80–100% intensity)**, which your Karvonen-calculated upper zones define. However, heart rate lags behind effort by 15–30 seconds, so during short HIIT intervals it may never reach the target before the interval ends. For HIIT, many coaches recommend using **perceived exertion (RPE 8–9 out of 10)** as the primary guide rather than relying solely on bpm.
VO₂ max — the maximum rate of oxygen your body can use during exercise — is closely linked to heart rate training. Consistent training in **Zone 3–4 (70–90%)** pushes your cardiovascular system to adapt, ultimately increasing VO₂ max over time. A higher VO₂ max typically correlates with a lower resting heart rate, meaning your Karvonen-calculated zones will shift as your fitness improves. Recalculate your THR every 4–8 weeks if your RHR changes significantly.
No. Pregnancy significantly changes cardiovascular physiology — cardiac output increases up to 50% by the third trimester. Standard MHR formulas and training zones are **not validated for pregnant individuals**. The American College of Obstetricians and Gynecologists (ACOG) recommends that pregnant women use the **Rating of Perceived Exertion (RPE) scale** (aiming for "somewhat hard," around 13–14 on the Borg scale) rather than fixed heart rate targets, and always exercise under obstetric supervision.
For fat burning, the generally recommended intensity is **60–70% of heart rate reserve** using the Karvonen formula. In this zone, your body preferentially uses fat as a fuel source. For a 35-year-old with an RHR of 62 bpm (as in our example), that equals roughly **135–147 bpm**. Note that higher-intensity intervals also burn significant calories and fat overall, so the "fat-burning zone" is not the only path to fat loss.
Place two fingers (index and middle) lightly on the inside of your wrist just below the thumb (radial pulse) or on the side of your neck (carotid pulse). Count the number of beats for **60 full seconds** — or count for 30 seconds and multiply by 2. Do this immediately after waking, before getting up, for the most accurate reading.
Yes, the Karvonen formula is appropriate for older adults and is generally considered **more accurate** than simple MHR-percentage methods for this age group, because it accounts for individual resting heart rate differences. However, older adults — especially those with heart conditions — should always consult a physician before beginning or intensifying an exercise regimen and may benefit from a clinical exercise stress test to determine true MHR.
A commonly cited **average resting heart rate for healthy adults is 70 bpm**. You can use this as a placeholder, but your personalized result will be less accurate. We strongly recommend measuring your actual RHR on a few consecutive mornings for the best training guidance.
**Maximum Heart Rate (MHR)** is the theoretical upper limit — the fastest your heart can beat during all-out effort. It is estimated (not a goal) and typically used only as a reference point. **Target Heart Rate (THR)** is the *range you aim to stay within* during a workout to achieve a specific training benefit, expressed as a percentage of your Heart Rate Reserve plus resting heart rate.
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