Target heart rate zones
Target heart rate zones divide exercise intensity into ranges of heart rate (beats per minute, bpm).
The idea is simple: once an estimated maximum heart rate is known, training zones can be expressed as
percentages of that maximum (or of heart-rate reserve). These zones are widely used in fitness planning to
describe “easy aerobic,” “moderate,” and “high-intensity” work, but they remain estimates rather than
direct physiological measurements.
Step 1: Estimate maximum heart rate
This calculator uses the common introductory estimate:
\[
HR_{\max}\approx 220-\text{age}
\]
where age is in years and \(HR_{\max}\) is in bpm. Individual maximum heart rate can differ substantially from
this estimate, so zone boundaries should be interpreted as approximate.
Method A (default): Percent of maximum heart rate
In the % of max method, a zone is defined by a lower and upper fraction of \(HR_{\max}\).
For a zone with percent range \(p_{\text{low}}\%\) to \(p_{\text{high}}\%\),
the heart-rate range is:
\[
\begin{aligned}
HR_{\text{low}} &= HR_{\max}\cdot \frac{p_{\text{low}}}{100}\\
HR_{\text{high}} &= HR_{\max}\cdot \frac{p_{\text{high}}}{100}
\end{aligned}
\]
Example (illustrative): if \(HR_{\max}=190\) bpm and the zone is 60–70%,
then \(HR_{\text{low}}=190\cdot 0.60=114\) bpm and
\(HR_{\text{high}}=190\cdot 0.70=133\) bpm.
Method B (advanced): Karvonen (Heart-Rate Reserve, HRR)
The Karvonen method uses the idea that training intensity is better represented as a percentage of
the heart-rate reserve, the difference between maximum heart rate and resting heart rate.
If resting heart rate \(HR_{\text{rest}}\) is known, define:
\[
HRR = HR_{\max}-HR_{\text{rest}}
\]
Then for any intensity fraction \(p\) (for example \(p=0.70\) for 70%), the target heart rate is:
\[
HR_{\text{target}} = (HRR \cdot p)+HR_{\text{rest}}
\]
For a zone with percent range \(p_{\text{low}}\%\) to \(p_{\text{high}}\%\), the zone boundaries are:
\[
\begin{aligned}
HR_{\text{low}} &= (HRR\cdot \frac{p_{\text{low}}}{100})+HR_{\text{rest}}\\
HR_{\text{high}} &= (HRR\cdot \frac{p_{\text{high}}}{100})+HR_{\text{rest}}
\end{aligned}
\]
Because \(HR_{\text{rest}}\) shifts the zone upward, Karvonen zones often differ from simple % of max zones,
especially when resting heart rate is relatively high or low.
Zone schemes
The calculator supports a standard 5-zone scheme (Zone 1 through Zone 5) defined by percent bands,
and it can also accept custom percent ranges. A typical 5-zone scheme (by % of max or by % of HRR) is:
\[
\begin{aligned}
\text{Zone 1: } & 50\%\text{–}60\%\\
\text{Zone 2: } & 60\%\text{–}70\%\\
\text{Zone 3: } & 70\%\text{–}80\%\\
\text{Zone 4: } & 80\%\text{–}90\%\\
\text{Zone 5: } & 90\%\text{–}100\%
\end{aligned}
\]
If custom ranges are entered, each line defines one zone using:
label, lowPercent, highPercent. Percent values are interpreted as intensities and must satisfy
\(0\le \text{lowPercent} < \text{highPercent}\le 100\).
How the calculator classifies a chosen target bpm
If a target heart rate is provided, the calculator checks which computed interval contains it and reports the
corresponding zone. Conceptually, for zones \([HR_{\text{low},i}, HR_{\text{high},i}]\),
it finds an index \(i\) such that:
\[
HR_{\text{low},i}\le HR_{\text{target}} < HR_{\text{high},i}
\]
(with the upper bound treated as inclusive for the last zone to avoid dropping a value equal to the maximum
boundary).
Interpreting the visualizations
-
Zone band bar: a single horizontal bar divided into segments for each zone. Each segment corresponds to a bpm
interval computed from your method and percent scheme.
-
Gauge/dial: shows the estimated \(HR_{\max}\) on a semicircle and places a needle at the chosen target bpm.
Moving the needle updates the target value and the highlighted zone.
-
Selected workout zone highlight: optionally highlights a chosen zone (or automatically highlights the zone
containing the target bpm).
Practical limitations and safety note
Heart-rate zones based on \(220-\text{age}\) and resting heart rate are convenient approximations, not medical
diagnostics. Hydration, temperature, medications, illness, stress, altitude, and fitness level can shift heart rate
responses. If there is chest pain, dizziness, unusual shortness of breath, or known cardiovascular risk, training
guidance should come from a qualified clinician.
