Beyond the Numbers: Special Training Intensities, Part 1 (Fatmax to Sweet Spot)
Fatmax, MAF, Zone 2, Tempo and Sweet Spot are named training intensities between the numbered zones. What each one is, where it sits, and when to use it.
Numbered zones map intensity from easy to all-out. Coaches and apps also use named intensities: Fatmax, MAF, Sweet Spot, Tempo. These are not a different zone system. They are targets on the same band, each defined by the adaptation it chases. A zone number tells you how hard. A name tells you why. Part 1 covers the aerobic end up to threshold. Part 2 covers threshold and above.
Fatmax: the peak fat-burning intensity
Where it sits: low aerobic, around the first lactate threshold (LT1), often near 60–65% of VO₂max.
What it is: the intensity at which you oxidise fat at the highest rate in grams per minute. Easier, and you burn a higher fraction of fat but less total. Harder, and you tip toward carbohydrate.
Why train it: metabolic efficiency. You teach the body to rely on fat stores and spare limited carbohydrate. It overlaps heavily with Zone 2. More on fat oxidation.
MAF: the aerobic threshold cap
Where it sits: around the aerobic threshold (LT1), the top of Zone 2.
What it is: Phil Maffetone's MAF (Maximum Aerobic Function) method estimates your aerobic ceiling as 180 minus your age, adjusted for health and training history.
Why train it: a conservative cap that keeps easy days easy, especially for beginners who drift too hard. It is a governor on aerobic work more than a separate workout. Adjustments are on the MAF 180 page.
Zone 2: the aerobic base
Where it sits: Z2 of a 5-zone model, ~60–70% of max heart rate, just below LT1.
What it is: easy, conversational aerobic effort. It has its own number in every system, but it is defined by purpose as much as position.
Why train it: to build mitochondria, capillaries and fat metabolism with volume you can repeat daily. See Zone 2 heart rate, explained and how to train Zone 2.
Tempo: comfortably hard
Where it sits: Zone 3, about 76–90% of FTP for cyclists, marathon-to-half-marathon effort for runners.
What it is: tempo is the effort you could hold for a long time but not all day. You can talk in short phrases.
Why train it: aerobic strength and muscular endurance, and race-pace efforts that feel sustainable. Too much of it becomes the "gray zone": tiring, but too easy for top-end gains. Use it in measured doses.
Sweet Spot: the high-value compromise
Where it sits: 88–94% of FTP, straddling the Zone 3/Zone 4 line.
What it is: the narrow band just below threshold that delivers a large share of threshold's benefit for less fatigue.
Why train it: to raise FTP efficiently when training time is limited. You can accumulate more Sweet Spot minutes per week than threshold minutes, as long as not every ride drifts into it. Full detail on the Sweet Spot training page.
Where they sit on the band
From easy to hard:
- Fatmax ≈ MAF ≈ aerobic threshold (LT1): top of easy
- Zone 2: easy aerobic, just below that line
- Tempo: comfortably hard, Zone 3
- Sweet Spot: top of tempo into low threshold, 88–94% FTP
They cluster and overlap rather than tiling the range. Set your bands with the heart-rate, power or pace calculators, then aim at these intensities within them.
Part 2 picks up at threshold: LT2/FTP/MLSS, the Norwegian sub-threshold method, Critical Power, VO₂max and the anaerobic top end.
Sources
- Jeukendrup and colleagues, fat oxidation and Fatmax
- Phil Maffetone, the MAF method
- Allen & Coggan, Training and Racing with a Power Meter (Sweet Spot, FTP-percentage bands)
- Seiler, intensity distribution
- San Millán, Zone 2 and mitochondrial function