In a recent a recent blogpost we dived into the fact that lactate threshold 1 (LT1) and FatMax (maximal fat oxidation rate - MFO) rarely is at the same power output. The conclusion to the blogpost was that FatMax-intensity, based on some real world examples from lab tests of cyclists, was highly individual.
Below is a short recap of FatMax training and why it's so important:
Training at or around FatMax-intensity will stimulate your fat burning capacity very effectively, and consequently improve your performance on the bike. Simply because an improved capacity to burn fat will spare your carbohydrate stores, leading to enhanced performance in the final hours of a race, where you need the carbs for the last decisive high intensity efforts!
Thus, improved fat oxidation capacity leads to better performance by making the body more aerobic flexible. Aerobic flexibility refers to the body's ability to shift between different fuel sources (fat and carbohydrates) depending on the intensity of exercise. A well-developed aerobic system allows cyclists to rely more on fat at higher intensities, effectively delaying glycogen depletion and improving endurance and fatigue resistance - durability.
Since FatMax training aims to enhance fat oxidation efficiency, it will improve your aerobic flexibility, which means you can maintain higher power outputs while still primarily using fat as fuel. This adaptation is crucial for cycling performance, as it allows for better energy conservation and over long rides and during races.
Here's how aerobic flexibility relates to FatMax:
Increased fat utilization at higher intensities – With better aerobic flexibility, a cyclist can rely on fat oxidation at higher power outputs, delaying carbohydrate depletion.
Efficient substrate shifting – The ability to transition smoothly between fat and carbohydrate metabolism based on intensity demands.
Lower lactate accumulation – Improved FatMax helps delay the onset of glycolysis (carbohydrate burning), keeping lactate levels lower at moderate intensities.
Improved metabolic efficiency – Training at FatMax intensity increases mitochondrial function, allowing for better energy production across different zones.
A very common belief among cyclists is that FatMax-intensity is more or less equal to the power output at the 2 mmol lactate threshold (LT1) or the first ventilatory threshold (VT1). These thresholds are often used to set the upper border of the endurance training intensity domain. In a classic 6-zone model often used in cycling, LT1/VT1 is often found in the upper part of zone 2 or lower part of zone 3.
But can we trust a FatMax training intensity based on set benchmarks such as thresholds (LT1 / VT1), functional threshold power (FTP) or heart rate? Or is it a misguided approach when trying to optimize fat oxidation and aerobic flexibility?
A very recent study by Meixner and colleagues looked into how FatMax-intensity correlates to a set threshold like LT1, VT1 or % of maximal heart rate (%HRmax) in 50 experienced cyclists (30 males and 20 females). The study concluded that using a set benchmark like the 2 mmol lactate concentration or 72-82 % HRmax lacks precision. Further the study found that in general FatMax-intensity is around 25 % lower than VT1.
'Our results indicate that relying on universal benchmarks can result in training loads that are either insufciently challenging or overly taxing, which can diminish training efectiveness'.
In other words if you want to train and improve your fat oxidation capacity, your FatMax-intensity needs to be determined directly. Thus giving you precise information on which intensity-range to stick to, in order to stimulate FatMax the most.
'FatMax, for instance, allows for precise targeting of intensities that optimize fat oxidation, an adaptation crucial for endurance per formance. This metric is particularly valuable for athletes aiming to enhance endurance, support glycogen sparing, or improve body composition'.
So based on the findings of the study, which is backed up by our experiences when testing cyclists, it's quite clear that you need to take an individual approach when determining FatMax.
FatMax has to be derived from a test that clearly determines the intensity where you have the highest maximal fat oxidation rate - otherwise your FatMax-training is just pure guess work!
On the graph below you can see an example from an INSCYD Lactate test on a female elite rider. The rider's FatMax was estimated to 152W (the power that elicits the highest fat oxidation rate) and LT1 to 173W - that's a difference of 21W. So a result that supports findings from the above mentioned study. As you also can see from the graph, the riders FatMax training zone is ranging from approximately 140 to 170W, which means that this intensty range is optimal for improving fat oxidation. So in this case the riders fat oxidation rate, will still be quite favorable at LT1 intensity. In this regard it's important to emphasize, that LT1 derived from an INSCYD test, is not a set benchmark like the commonly used 2 mmol threshold. It's derived from a method based on individual lactate kinetics.
To sum up.....
If you want to be sure to know your FatMax power output, you need to do a proper performance test, that will give you a full picture of your metabolic profile - e.g. an INSCYD PPD Test or Lactate Test.
References:
Maunder E, Plews DJ and Kilding AE. Contextualising Maximal Fat Oxidation During Exercise: Determinants and Normative Values. Front. Physiol., 23, 9 (2018).
Ferri Marini, C.; Tadger, P.; Chávez-Guevara, I.A.; Tipton, E.; Meucci, M.; Nikolovski, Z.; Amaro-Gahete, F.J.; Peric, R. Factors Determining the Agreement between Aerobic Threshold and Point of Maximal Fat Oxidation: Follow-Up on a Systematic Review and Meta-Analysis on Association. Int. J. Environ. Res. Public Health 20, 453 (2023).
Meixner B, Filipas L, Holmberg HC, Sperlich B. Zone 2 Intensity: A Critical Comparison of Individual Variability in Different Submaximal Exercise Intensity Boundaries, Translational Sports Medicine, 2025, 2008291, 14 pages, (2025).
Purdom, T., Kravitz, L., Dokladny, K. et al. Understanding the factors that effect maximal fat oxidation. J Int Soc Sports Nutr 15, 3 (2018).
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