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 Ahrens2026年6月12日最終更新 2026年9月6日

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:

乳酸性作業閾値心拍数

165bpm

サイクリングのLTHR

ゾーン	範囲	鍛えられるもの
Z1	アクティブリカバリー ≤ 132 bpm	リカバリー走。脚をほぐします。 RPE 1〜2、非常に楽。
Z2	エンデュランス 133–147 bpm	有酸素的土台と脂質代謝。 RPE 3〜4、一日中続けられるペース。
Z3	テンポ 148–153 bpm	有酸素的持久力、「スイート」な定常運動。 RPE 5〜6、快適にきつい。
Z4	スレッショルド 154–163 bpm	乳酸性作業閾値、持続可能なきつさ。 RPE 7〜8、20〜60分が限界。
Z5a	VO₂max 164–168 bpm	最大有酸素パワー。 RPE 9、3〜8分の運動。
Z5b	無酸素性容量 169–175 bpm	無酸素性容量、短く鋭く。 RPE 9〜10、30秒〜3分。
Z5c	神経筋 ≥ 176 bpm	スプリントパワーと神経筋の駆動。 RPE 10、全力。

アクティブリカバリー

≤ 132 bpm

エンデュランス

133–147 bpm

テンポ

148–153 bpm

スレッショルド

154–163 bpm

Z5a

VO₂max

164–168 bpm

Z5b

無酸素性容量

169–175 bpm

Z5c

神経筋

≥ 176 bpm

Z1 · アクティブリカバリー. リカバリー走。脚をほぐします。 RPE 1〜2、非常に楽。

Z2 · エンデュランス. 有酸素的土台と脂質代謝。 RPE 3〜4、一日中続けられるペース。

Z3 · テンポ. 有酸素的持久力、「スイート」な定常運動。 RPE 5〜6、快適にきつい。

Z4 · スレッショルド. 乳酸性作業閾値、持続可能なきつさ。 RPE 7〜8、20〜60分が限界。

Z5a · VO₂max. 最大有酸素パワー。 RPE 9、3〜8分の運動。

Z5b · 無酸素性容量. 無酸素性容量、短く鋭く。 RPE 9〜10、30秒〜3分。

Z5c · 神経筋. スプリントパワーと神経筋の駆動。 RPE 10、全力。

LTHRベースのゾーンは、年齢推定ではなく実際の閾値に基づくため、%HRmaxよりも個別性が高くなります。サイクリングとランニングのLTHRは異なるので、各競技を別々にテストしてください。
フィールドテスト：ウォームアップ後、きつい30分のソロタイムトライアルを走るか漕ぎます。LTHRは最後の20分の平均心拍数です（Frielのプロトコル）。

パーソナライズされた結果のPDFと、いつでも再表示できるQRコード付き。

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.