Friel Heart Rate Zone Calculator
Turn a sport-specific lactate threshold heart rate into Joe Friel cycling or running zones, with whole-bpm boundaries and session planning.| Zone | % of LTHR | Heart rate | Training emphasis | Copy |
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Training zones turn a measured threshold into repeatable intensity ranges. Joe Friel's heart-rate method starts with lactate threshold heart rate (LTHR), the heart rate associated with a hard, sustainable effort, and expresses seven zones as percentages of that threshold. It does not start with maximum heart rate or an age-based estimate.
Running and cycling need separate settings. The same athlete may record different threshold heart rates in the two sports, and Friel's lower-zone percentage cutoffs also differ. A cycling threshold should therefore produce cycling zones, while a running threshold should produce running zones.
| Value | Use | Important limit |
|---|---|---|
| LTHR | Sets every Friel zone boundary for one sport. | It should come from a recent sport-specific test, race, lab, or coaching assessment. |
| Current heart rate | Shows which computed zone contains a reading. | Sensor lag and error can make a brief reading misleading. |
| Session duration | Turns an illustrative percentage mix into minutes by zone. | The mix is a planning sketch, not an official Friel workout prescription. |
Heart rate changes with heat, altitude, hydration, fatigue, illness, medication, stress, and sensor quality. Zones are useful training guides, not medical limits or guarantees of a physiological state. Anyone with symptoms, a medical condition, or uncertainty about strenuous testing should seek qualified guidance before attempting a threshold test or hard session.
How to Use This Tool:
Use one recent LTHR from the same sport as the training session.
- Choose Cycling or Running. Do not reuse one sport's threshold merely because the workouts feel similar.
- Enter Lactate threshold heart rate from a known assessment, or use the final 20-minute average from a properly paced 30-minute field test. The source choice records provenance and does not apply another conversion.
- Optionally enter Current heart rate to locate a reading. Add a session duration and Illustrative session focus only when a minutes-by-zone sketch is useful.
- Review the whole-bpm boundaries, transfer them to the matching sport profile, and compare hard-session targets with perceived effort, pace or power, recovery, and coaching or clinical advice.
Interpreting Results:
The seven Zone bands are threshold-relative ranges, not seven separate measurements. A whole-bpm boundary belongs to the higher zone. At a cycling LTHR of 160 bpm, for example, 130 bpm enters Z2 because it is the first whole number at or above 81% of threshold.
A current reading identifies only the matching band. It does not confirm workout quality, safety, or whether the heart-rate sensor captured a stable effort. Treat the optional session plan as a draft distribution and adapt it to the intended workout, recent recovery, and the plan or coach being followed.
Technical Details:
Zone membership is determined from the exact ratio of current heart rate to LTHR. Whole-bpm display boundaries are derived afterward, so rounding never creates a gap or overlap between adjacent zones.
Formula Core:
For each cutoff ratio r, the first whole beat in the higher zone is the mathematical ceiling of the exact threshold product.
L is sport-specific LTHR in beats per minute, r is a decimal cutoff, Br is the higher zone's entry boundary in whole bpm, and H is an optional current heart rate. When no cutoff is greater than H/L, the reading is in Z5c.
Rule Core:
| Zone | Cycling | Running | General training cue |
|---|---|---|---|
| Z1 | <81% LTHR | <85% LTHR | Recovery and very easy aerobic work |
| Z2 | ≥81% and <90% | ≥85% and <90% | Aerobic endurance |
| Z3 | ≥90% and <94% | ≥90% and <95% | Steady or tempo work |
| Z4 | ≥94% and <100% | ≥95% and <100% | Sub-threshold work |
| Z5a | ≥100% and <103% | ≥100% and <103% | Work just above threshold |
| Z5b | ≥103% and <107% | ≥103% and <107% | Hard aerobic-capacity intervals |
| Z5c | ≥107% LTHR | ≥107% LTHR | Very hard anaerobic efforts |
At 160 bpm cycling LTHR, the zone floors are 0, 130, 144, 151, 160, 165, and 172 bpm. The corresponding ceilings are 129, 143, 150, 159, 164, 171, and 260 bpm within the optional current-reading input range.
The optional session plan multiplies total minutes by one illustrative planning distribution. These percentages do not change the zone boundaries.
| Focus | Z1 | Z2 | Z3 | Z4 | Z5a | Z5b | Z5c |
|---|---|---|---|---|---|---|---|
| Recovery | 70% | 30% | 0% | 0% | 0% | 0% | 0% |
| Endurance base | 20% | 55% | 15% | 10% | 0% | 0% | 0% |
| Tempo | 15% | 25% | 40% | 15% | 5% | 0% | 0% |
| Threshold | 10% | 20% | 25% | 25% | 15% | 5% | 0% |
| VO2 / 5K | 10% | 15% | 15% | 20% | 20% | 20% | 0% |
LTHR accepts 90 to 230 bpm. Current heart rate accepts 0 to 260 bpm, where zero omits the lookup. Session duration accepts 0 to 600 minutes, where zero omits the plan. All boundaries are recalculated when sport or LTHR changes.
Health, Privacy, and Accuracy Notes:
The zones are informational training estimates and do not provide medical clearance, diagnosis, or treatment. Do not use them to override symptoms or professional advice. A field test is strenuous and may be unsuitable for some people. Inputs are evaluated in the browser and no server-assisted calculation is used, but any copied or downloaded record should be handled according to its sensitivity.
References:
- Joe Friel's Quick Guide to Setting Zones, TrainingPeaks, originally published 2009.
- Lactate Profile, UC Davis Sports Medicine.