Beyond the Numbers: Special Training Intensities, Part 1 (Fatmax to Sweet Spot)

The numbered training zones, Z1 to Z5 or Z1 to Z7, are a map of intensity from easy to all-out. But you'll constantly hear coaches and apps talk about intensities with names instead of numbers: Fatmax, MAF, Sweet Spot, Tempo. These aren't a different zone system. They're destinations on the same band, specific intensities that often sit between or across the numbered zones, each defined by the adaptation it targets rather than by where it falls. This two-part series maps the most useful of them. Part 1 covers the aerobic-to-tempo end, from the slowest fat-burning effort up to the edge of threshold. (Part 2 covers threshold and above.)

The reason these named intensities exist is simple. A number like "Zone 3" tells you how hard, but not why. "Sweet Spot" tells you the purpose. Think of the numbers as the ruler and the names as the targets you aim the ruler at.

Fatmax: the peak fat-burning intensity

Where it sits: low aerobic, around your first lactate threshold (LT1), roughly the top of an easy effort, often near 60–65% of VO₂max.

What it is: Fatmax is the exercise intensity at which your body oxidises fat at the highest rate (grams per minute). Go easier and you burn a higher fraction of fat but less total; go harder and you tip toward carbohydrate. The peak, the "Fatmax," sits in between, in the easy aerobic range.

Why train it: to build metabolic efficiency. You teach your body to rely on its near-limitless fat stores and spare its limited carbohydrate. It overlaps heavily with Zone 2 and is the metabolic reason easy aerobic volume matters. More on fat oxidation as fuel.

MAF: the aerobic threshold cap

Where it sits: right around the aerobic threshold (LT1), the same neighbourhood as Fatmax and the top of Zone 2.

What it is: the MAF (Maximum Aerobic Function) method, from Phil Maffetone, estimates your aerobic ceiling as 180 minus your age, adjusted up or down for health and training history. Train at or below that heart rate and you stay reliably aerobic.

Why train it: as a conservative, hard-to-game cap that keeps easy days genuinely easy. It's especially useful for beginners who otherwise drift too hard. It's less a separate workout than a governor on your aerobic work. Walk through the adjustments 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: the famous one. Easy, conversational aerobic effort. It earns its own number in every system, but it belongs here because it's defined by purpose as much as position.

Why train it: to build the aerobic engine (mitochondria, capillaries, fat metabolism) with volume you can repeat day after day. It's the foundation everything harder is built on. We cover it in depth in Zone 2 heart rate, explained and how to actually train Zone 2.

Tempo: comfortably hard

Where it sits: between endurance and threshold, roughly Zone 3, about 76–90% of FTP for cyclists, or "marathon-to-half-marathon" effort for runners.

What it is: tempo is the "comfortably hard" effort you could hold for a long-ish time but not all day. You can still talk, but only in short phrases. It sits above easy aerobic work and below true threshold.

Why train it: to build aerobic strength and muscular endurance, and to make race-pace efforts feel more sustainable. One caution: spend too much time here and it becomes the "gray zone," hard enough to tire you, not hard enough to drive top-end gains. Use it deliberately, in measured doses.

Sweet Spot: the high-value compromise

Where it sits: the top of tempo into the bottom of threshold, specifically 88–94% of FTP, straddling the Zone 3/Zone 4 line.

What it is: Sweet Spot is the narrow band just below threshold that delivers a large share of threshold's training benefit for noticeably less fatigue. That ratio of lots of stimulus for manageable cost is why time-crunched cyclists love it.

Why train it: to raise FTP efficiently when training time is limited. You can accumulate more Sweet Spot minutes per week than you could at full threshold, so it's a productive workhorse intensity, as long as you don't let every ride drift into it. Full detail on the Sweet Spot training page.

Where they sit on the band

From easy to hard, the aerobic-end named intensities line up like this:

• Fatmax ≈ MAF ≈ aerobic threshold (LT1): top of easy, the metabolic-efficiency neighbourhood
• Zone 2: easy aerobic, just below that line
• Tempo: comfortably hard, mid-band (Zone 3)
• Sweet Spot: top of tempo into low threshold (88–94% FTP)

Notice they cluster, overlap, and don't tile the whole range, because they're purpose-built targets, not a tidy partition. Set your own zone bands first with the heart-rate, power or pace calculators, then aim at these named 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

Fat-oxidation and Fatmax concepts follow Jeukendrup and colleagues. The MAF method is Phil Maffetone's. Sweet Spot and the FTP-percentage bands follow Allen & Coggan, Training and Racing with a Power Meter. The aerobic-base rationale draws on Seiler (intensity distribution) and San Millán (Zone 2 and mitochondrial function).