FatMax
FatMax is the exercise intensity at which fat oxidation reaches its maximum, typically located in lower zone 2 or the low-intensity training range.
Definition
“FatMax” is the exercise intensity at which fat oxidation reaches its maximum, together with the amount of fat oxidised there in grams per hour. The point typically lies in lower zone 2 or the LIT range. It is regarded as a central marker of metabolic health and aerobic capacity.
Why it matters
The course of the substrate curve in a diagnostic reveals the state of a body. If maximal fat oxidation occurs right at the onset of movement and only declines from there, the suspicion is that either endurance capacity is low or the body is approaching overtraining and already in a state of physical burnout.
The amount of fat oxidised at the maximum also gives a good impression of an athlete’s general performance class.
| FatMax (g/h) | Performance level | Description |
|---|---|---|
| < 10 | Very low / metabolically inefficient | Hardly any fat metabolism active; typical of inactivity or disorders |
| 10–20 | Low | Untrained or metabolically restricted (e.g. Hashimoto’s, long Covid) |
| 20–30 | Moderate | Recreational athlete, limited metabolic flexibility |
| 30–45 | Advanced | Good baseline oxidation, trained metabolism |
| 45–60 | Very good | Semi-professionals, good mitochondrial function |
| 60–75 | Excellent | Professionals, high metabolic efficiency and training status |
| > 75 | Elite endurance athletes | World class, e.g. keto-adapted or genetically favoured |
Athletes who know their FatMax range can place long sessions exactly where fat metabolism receives the greatest stimulus and save carbohydrate for the intensities above CarbMax.
How obseed measures it
FatMax can only be determined through metabolic diagnostics with breath-gas analysis. From oxygen uptake and carbon dioxide output the respiratory exchange ratio is calculated per stage, and from that fat and carbohydrate oxidation in grams per hour. obseed stores power, heart rate and fat quantity at FatMax in the performance values and evaluates recorded sessions against this range.
It must not be forgotten that power output alone says nothing about the underlying metabolism. Calculating a fictitious FatMax range from a functional threshold power is grossly negligent and can lead to lasting damage. The “fat-burning zones” of sports watches, too, are percentages of maximal heart rate and have nothing to do with measured substrate use.
Example
A 62 kg athlete completes a step test. At 140 W and 132 bpm spiroergometry measures a fat oxidation of 0.58 g/min.
Fat oxidation: 0.58 g/min × 60 = 34.8 g/h
Energy from fat: 34.8 g/h × 9.4 kcal/g ≈ 327 kcal/h
Classification: 30–45 g/h → advancedHer FatMax range therefore sits at roughly 125 to 150 W or 125 to 138 bpm. A four-hour base ride in this range covers about 1,300 kcal from fat; the rest of the energy requirement has to come from glycogen and fuelling. If the next test shows 42 g/h at 155 W, not only power but also metabolic flexibility has improved.
Categories
- Diagnostik
- Technische Begriffe