Training Fatmax Without Testing It

William Horkoff
Sep 24, 2025
2 min read

Updated: Sep 24, 2025

For trained amateurs, Fatmax ≈ ~60–70% of FTP or ~65–75% HRmax, typically landing near ~72% HRmax and below VT1. That tracks with a 2025 study (Meixner et al.) and earlier Maunder/Plews work. Elite outliers can sit closer to VT1 don’t blindly copy though with that being said.

Why care?

Durability improves when you spare glycogen. Fat is the bottomless pit; carbs aren’t. Training near Fatmax targets the peak fat-oxidation zone, which should help preserve carbs later. Note: no study has definitively proved that Fatmax training alone improves durability but the logic is sound and widely used in the field.

Where does Fatmax sit?

Meixner 2025: In 50 trained cyclists (VO₂max ~54), Fatmax < VT1 and clustered near ~72% HRmax. VT1 lined up closer to ~82% HRmax and ~2.0 mmol/L lactate. Participants took 35 g carbs pre-test, i.e., a real-world fueling context.

Maunder et al. 2018: Big dataset suggests Fatmax ≈ ~56% VO₂max, which translates roughly to ~60–70% FTPor ~65–75% HRmax.

Practical setup (INSCYD

I will conduct a INSCYD PPD test with athletes to get this information as it can be useful in determining Fatmax & the appropriate intensity that corresponds.

Practical setup (no lab)

Anchor the target:
HR: set a working band = 65–75% HRmax (start at ~72%).
Power: 60–70% FTP if your FTP is current and legit.
Field verification (decoupling check):
Ride 40–60 min steady in that band. If HR drifts <5% vs power/pace (i.e., minimal decoupling) and RPE ≤ 3–4/10, you’re in the zone. Big drift? Back off 3-5 bpm next time.
Simple step test (optional):
After a warm-up, do 3×8 min at ~58%, ~64%, ~70% FTP (or HR equivalents). Note breathing, RPE, HR drift. The “sweet” step = easy breathing, steady HR.
Elite caveat: Pros and high responders may place Fatmax closer to VT1 (sometimes overlapping). Validate with decoupling, RPE, and if you have it lactate or SmO₂.

How to train it (40–120 min)

2–4×/wk in race-build or early base:
- Short days: 40–60 min continuous at Fatmax.
- Long day: 75–120 min at Fatmax, optionally bookended by easy Z1.
Fueling: Don’t starve it. 20-40 g carbs/hr on shorter sessions; 40–60 g/hr on longer. Fat oxidation stays high below VT1 even when fueled. You’re training, not auditioning for a keto cult. Progression: Add time before intensity. When 60 min is rock-solid (low drift), stretch duration or add gentle upper-aerobic floats (5–10 min just below VT1).

Common mistakes

Using a stale FTP → your “60–70%” is fantasy land.
Chasing a single magic bpm instead of a range.
Doing “Fatmax” after 5 espressos and no food, then calling the dizziness “metabolic flexibility.”
Mixing ratios in the same session (on IG and on the bike). Consistency = clarity.

References (in plain English)

Maunder, Kilding, Plews (2018) Ironman substrate metabolism + contextualizing max fat oxidation.

Meixner et al. (2025) showed Fatmax sits lower than VT1 and is near ~72% HRmax; VT1 ~2 mmol and ~82% HRmax.