Workout guides Effort & zones
Heart Rate Zones Explained
Heart rate zones divide exercise intensity into ranges. A zone number only makes sense with its calculation method: Zone 2 based on maximum heart rate can have different boundaries from Zone 2 based on lactate threshold heart rate.
By Aika · Reviewed
What a heart rate zone describes
A heart rate zone is a range used to organize intensity. The number on its label is only part of the instruction: you also need the calculation method, the reference value and sometimes the sport. “Thirty minutes in Zone 2” is incomplete until those are known.
Heart rate, pace and power are different measurements. A pace target specifies how quickly you cover distance; a power target specifies output; a heart rate target describes a physiological response. Their zone numbers are not universal equivalents.
A named five-zone example: Polar’s HRmax model
Polar’s five-zone maximum-heart-rate model divides 50–100% of HRmax into the following ranges. These are this model’s boundaries, not a definition shared by every device.
| Zone | % of HRmax | Polar intensity label |
|---|---|---|
| 1 | 50–60% | Very light |
| 2 | 60–70% | Light |
| 3 | 70–80% | Moderate |
| 4 | 80–90% | Hard |
| 5 | 90–100% | Maximum |
Source: Polar: Heart Rate Zones.
The percentages describe ranges, not personal targets supplied by this article. Their accuracy depends on the reference maximum and configuration. Use your chosen system’s treatment of boundary values.
What Zone 2 means in that system
In the Polar example, Zone 2 means 60–70% of maximum heart rate. As a calculation example only, a reference HRmax of 190 gives 114–133 beats per minute. Changing the reference changes the result, even before you change the zone method.
That calculation should not be carried over to a plan using a different system. The useful question is “Which Zone 2 does this workout mean?” rather than assuming there is one range for every athlete and device.
Maximum heart rate vs threshold-based zones
HRmax is a maximum reference. Lactate threshold heart rate (LTHR) is a different intensity reference used by some training methods. A percentage of LTHR is not the same calculation as that percentage of HRmax.
For example, Joe Friel’s running zones use 85–89% of LTHR for Zone 2, while his cycling Zone 2 uses 81–89% of LTHR. This also illustrates why the sport matters.
Source: Joe Friel: Setting Training Zones.
| Illustrative method | Reference | Calculation |
|---|---|---|
| Polar HRmax model | HRmax 190 bpm | 60–70% → 114–133 bpm |
| Friel running LTHR model | LTHR 170 bpm | 85–89% → approximately 145–151 bpm |
These deliberately chosen example inputs demonstrate arithmetic; they are not your measured values or a recommendation to replace your current zones. Neither reference can be inferred from the other number in this table.
“Aerobic threshold” and “lactate threshold” also need context: the former commonly refers to a lower transition, while named lactate-threshold methods use their own reference criteria. A watch’s boundary is not automatically a measured threshold. Aerobic and anaerobic energy supply overlap rather than switching on and off between numbered zones.
Why watches can show different boundaries
Different ranges can come from different methods, input values, sport profiles or manual edits. Apple describes its five Heart Rate Zones as personalized using health data and also allows manual limits. That does not establish that their exact boundaries must match the Polar table.
Source: Apple: Heart Rate Zones on Apple Watch.
When comparing a plan with a watch, check the reference type, the stored maximum or threshold, the selected sport and any custom boundaries. Matching the number “2” on both screens is not enough to confirm that they mean the same intensity range.
Timing a session without measuring heart rate
Keep duration and intensity as separate instructions. In “30 minutes in Zone 2”, the timer supplies the thirty-minute window; the chosen heart rate system supplies the target range and reading.
Use Aika to time that window or the work and rest blocks specified by your plan. Use a separate heart rate device or app to monitor the zone. Setting a timer does not measure heart rate or verify that the intended intensity was maintained.
If your program uses perceived effort instead, identify its scale before comparing it with zones. The RPE guide explains why a lifting RPE cannot be converted directly into a heart rate target. The workout glossary covers the remaining abbreviations.
Common questions
Is Zone 2 always 60–70% of maximum heart rate?
That is the Zone 2 range in the Polar maximum-heart-rate example on this page. Other systems use different references and boundaries, so the label alone is insufficient.
Why are my running and cycling zones different?
Some methods set separate sport-specific threshold values and zone boundaries. Use the zones for the sport and method specified by the training plan.
Is heart rate Zone 2 the same as power Zone 2?
No. Heart rate measures a physiological response; power measures output. Their zone labels belong to different scales and do not form a universal one-to-one conversion.
Can Aika measure my heart rate zones?
Use Aika to time the work and recovery periods. This guide uses a separate heart rate device or app for heart rate readings and zone boundaries.