Friel's Heart-Rate Zones: 5, 7, and Why Every Platform Numbers Them Differently

Joe Friel's LTHR zones explained: the 5-zone model, the 5a/5b/5c split that makes it 7, how intervals.icu renumbers them, and how to test your LTHR.

Sven Ahrens2026년 6월 12일마지막 업데이트 2026년 9월 6일

heart rateLTHRFrieltraining zonesintervals.icu

If your zones from one app don't match another, Joe Friel's heart-rate model is usually why. It is the most used heart-rate zone system in endurance sport, and the most relabelled. Here is why it is 5 zones or 7, and how intervals.icu relabels them.

What Friel's zones are

Friel's zones are anchored to your lactate-threshold heart rate (LTHR), the heart rate you can hold for roughly an hour of hard, steady effort. Every band is pinned to a marker you measure, not to 220 − age (off by ±10–12 bpm).

Friel publishes separate cycling and running boundaries, since running LTHR sits a few percent above cycling LTHR.

Five zones, or seven?

Both. The model is five zones, but Friel splits Zone 5 into 5a, 5b and 5c, so it is most often shown as seven. Zones 1–4 are identical in either view:

Z1 Recovery
Z2 Aerobic / endurance
Z3 Tempo
Z4 Threshold (94–99% LTHR cycling, 95–99% running)
Z5a just above threshold
Z5b VO₂max / aerobic capacity
Z5c anaerobic, short and sharp

Plug in your LTHR and toggle between the 5- and 7-zone views:

젖산 역치 심박수

165bpm

사이클링 LTHR

존	범위	무엇을 단련하는가
Z1	능동적 회복 ≤ 132 bpm	회복용 스핀; 다리를 풀어줍니다. RPE 1–2, 매우 쉬움.
Z2	지구력 133–147 bpm	유산소 기초와 지방 대사. RPE 3–4, 하루 종일 갈 수 있는 페이스.
Z3	템포 148–153 bpm	유산소 지구력, '스위트'한 꾸준한 운동. RPE 5–6, 편안하게 힘듦.
Z4	역치 154–163 bpm	젖산 역치; 지속 가능한 강도. RPE 7–8, 20–60분 한계.
Z5a	VO₂max 164–168 bpm	최대 유산소 파워. RPE 9, 3–8분 노력.
Z5b	무산소 능력 169–175 bpm	무산소 능력, 짧고 날카로운 노력. RPE 9–10, 30초–3분.
Z5c	신경근 ≥ 176 bpm	스프린트 파워와 신경근 구동력. RPE 10, 전력 질주.

능동적 회복

≤ 132 bpm

지구력

133–147 bpm

템포

148–153 bpm

역치

154–163 bpm

Z5a

VO₂max

164–168 bpm

Z5b

무산소 능력

169–175 bpm

Z5c

신경근

≥ 176 bpm

Z1 · 능동적 회복. 회복용 스핀; 다리를 풀어줍니다. RPE 1–2, 매우 쉬움.

Z2 · 지구력. 유산소 기초와 지방 대사. RPE 3–4, 하루 종일 갈 수 있는 페이스.

Z3 · 템포. 유산소 지구력, '스위트'한 꾸준한 운동. RPE 5–6, 편안하게 힘듦.

Z4 · 역치. 젖산 역치; 지속 가능한 강도. RPE 7–8, 20–60분 한계.

Z5a · VO₂max. 최대 유산소 파워. RPE 9, 3–8분 노력.

Z5b · 무산소 능력. 무산소 능력, 짧고 날카로운 노력. RPE 9–10, 30초–3분.

Z5c · 신경근. 스프린트 파워와 신경근 구동력. RPE 10, 전력 질주.

LTHR 기반 존은 나이 추정치가 아닌 실제 역치에 기준을 두므로 %HRmax보다 더 개인화되어 있습니다. 사이클링과 러닝의 LTHR은 다르므로 종목별로 따로 테스트하세요.
필드 테스트: 워밍업 후 강도 높은 30분 단독 타임 트라이얼을 라이딩하거나 달립니다. LTHR은 마지막 20분의 평균 심박수입니다(Friel 프로토콜).

당신의 개인 맞춤 결과가 담긴 PDF와, 언제든 다시 열 수 있는 QR 코드.

Why every platform renumbers them

The boundaries are Friel's. The labels are not standardized.

intervals.icu uses the same Friel LTHR percentages but numbers the zones sequentially, Z1 to Z7. Friel's Z5a, Z5b and Z5c appear as Z5, Z6 and Z7.
TrainingPeaks, which Friel co-founded, keeps the original Z5a / Z5b / Z5c notation.

Same maths, different counting. If your zones "don't match", one tool split Zone 5 into a/b/c and the other counted to 7.

What the model gets right

It's individual. LTHR is your measured threshold, not a population average scaled by age.
It's measurable without a lab. A 30-minute time trial gives a usable number for free.
It's threshold-pinned. The zones stay sensible even as an age-based HRmax estimate drifts.
It's sport-specific. Separate cycling and running anchors stop you training one sport with the other's zones.

Where it falls short

Heart rate is blunt at the top end:

HR lags and drifts. It rises slowly at the start of an interval, climbs over a long effort (cardiac drift), and spikes in heat or dehydration.
It saturates above threshold. In Z5a–Z5c the heart-rate differences are tiny and arrive late. Power (cycling) or pace (running) controls those efforts far better. Friel himself moved toward power for the high zones.
It's a single-threshold model. It marks the upper threshold but not the lower aerobic threshold the way dual-threshold and polarized models do.
It's only as good as your test. A stale or badly paced LTHR test mis-sets every zone.

How to find your LTHR

The classic Friel field test:

Warm up 10–15 minutes easy with a couple of short pickups.
Time-trial for 30 minutes, solo, flat or on a trainer, hard and evenly paced.
Press lap at 10 minutes, so your monitor averages the final 20 minutes separately.
Your LTHR is the average heart rate of those last 20 minutes.

Test rested, separately for cycling and running. Re-test every 4–8 weeks of focused training. Then use the LTHR zone calculator, or compare against your max-heart-rate and %HRmax zones.