Original episode & show notes | Raw transcript
In the world of endurance sports, athletes and coaches are perpetually searching for a competitive edge. This has led to a deep interest in manipulating the body’s fuel systems. A popular concept that emerged from this is FatMax, which is theoretically the exercise intensity at which the body’s rate of fat oxidation is at its absolute highest.
The idea is seductive: if carbohydrates are the limiting factor in long-duration performance, then training the body to become exceptionally good at using its vast fat stores should, in theory, spare precious glycogen and lead to superior endurance. This concept has led many to believe that training specifically at their FatMax intensity is a shortcut to enhanced aerobic fitness and more effective weight loss.
However, the podcast “Empirical Cycling” argues that this belief is a misconception—a “FatMax Fallacy.” While the physiological state of FatMax is real, its application as a special training zone is based on a misunderstanding of how the body adapts to exercise and manages energy balance. This document will unpack the two central fallacies discussed in the podcast.
The most pervasive belief is that specifically targeting your FatMax zone during training will lead to greater improvements in fat metabolism and overall aerobic fitness than standard endurance training. The podcast argues that this is not the case because the primary drivers of aerobic adaptation are not tied to the type of fuel you are burning, but to the process of exercise itself.
To understand why this is, we must look at the fundamental order of operations within a muscle cell during exercise.
The Demand: A nerve impulse signals the muscle to contract.
The Action: The sarcoplasmic reticulum releases calcium ions (Ca2+). This allows muscle filaments (actin and myosin) to interact, causing a contraction. This mechanical action directly consumes ATP (adenosine triphosphate), the cell’s universal energy currency.
The Response: The muscle’s metabolic machinery works to regenerate the consumed ATP. It doesn’t inherently “care” where the ATP comes from—whether it’s regenerated via glycolysis (carbohydrates) or beta-oxidation (fats). The critical factor is the rate of demand. High-intensity work demands fast ATP regeneration, favoring carbohydrates. Low-to-moderate intensity work allows the slower, more sustainable fat oxidation pathways to contribute significantly.
The key insight is that the adaptations we seek—like building more mitochondria (mitochondrial biogenesis)—are triggered by signals related to the stress of the muscle contraction itself, not by the fuel source used. The podcast highlights two of the most well-understood signaling pathways:
Elevated Intracellular Calcium (Ca2+): The repeated release of calcium during muscle contractions is a powerful signal. Even slightly elevated calcium levels, sustained over a long duration (as in an endurance ride), activate a cascade of genetic machinery, most notably through a key regulator called PGC-1-alpha. This master switch promotes the building of new mitochondria and the enhancement of aerobic pathways.
AMPK Activation: As ATP is used, it breaks down into ADP and AMP. A rising concentration of AMP activates a crucial cellular energy sensor called AMP-activated protein kinase (AMPK). AMPK’s job is to restore energy homeostasis. It does this by turning off energy-consuming anabolic processes (like storage) and turning on energy-producing catabolic processes (like the burning of fats and carbohydrates). Like calcium, AMPK also signals through PGC-1-alpha to stimulate mitochondrial biogenesis.
Therefore, the duration and intensity of muscle contractions—which dictate the extent of calcium signaling and AMPK activation—are what truly drive aerobic improvement. Whether you are burning 0.5 grams of fat per minute or 0.8 grams of fat per minute during that time is largely irrelevant to the adaptive signal. A four-hour ride will always produce a greater adaptive stimulus than a two-hour ride at the same intensity, regardless of the precise fat-to-carb ratio burned.
This is why ketogenic diets, as discussed in a previous podcast episode, fail to improve performance. While they dramatically increase the markers for fat transport and oxidation, they don’t provide an additional adaptive stimulus beyond what normal training provides, and they compromise the ability to perform high-intensity work.
The second fallacy is that to lose body fat, one must specifically train in a zone that burns the most fat. This appeals to common sense but ignores the fundamental laws of thermodynamics and the body’s holistic energy balance.
Weight loss is governed by a simple, albeit challenging, principle: you must expend more energy (calories) than you consume. The body is an expert accountant. If it ends the day in a caloric deficit, it must retrieve the missing energy from its stores. Its largest and most energy-dense storage depot is body fat.
The crucial point is that the body doesn’t care how the deficit was created.
You can create a deficit by eating less while being sedentary. Your body will still tap into fat stores to fuel its basic metabolic functions.
You can create a deficit through high-intensity interval training (HIIT), which primarily burns carbohydrates. The large caloric expenditure and post-exercise oxygen consumption (EPOC) contribute to a daily deficit, which is then balanced by drawing from fat stores during periods of rest.
You can create a deficit through a long endurance ride.
The podcast illustrates this with a clear example: an elite athlete might burn 1 gram of fat per minute at their FatMax. Over a 5-hour (300-minute) ride, that’s 300 grams of fat, which equates to roughly 2,700 calories. However, this does not mean the athlete has lost 300 grams of body fat. They have simply created a large energy deficit. If they replenish those 2,700 calories with carbohydrates, proteins, or fats, the body will happily restore its fat stores. To achieve a net loss of fat, they must maintain an overall caloric deficit over time.
Therefore, the most effective exercise for weight loss is the one that sustainably burns the most total calories, not the one that burns the highest percentage of calories from fat. A longer or slightly more intense workout that burns more total calories will be more effective for fat loss than a shorter workout performed strictly at FatMax, even if the latter burns a higher proportion of fat during the activity itself.
The concept of FatMax is a valid physiological measurement. It describes a real phenomenon. However, its popular interpretation as a “magic” training zone is a fallacy.
For Adaptation: The benefits attributed to FatMax training are simply the benefits of endurance training. The adaptations are driven by the duration and stress of muscle contractions, not the specific fuel mix. The FatMax zone for most trained athletes is a wide range of intensities that heavily overlaps with their Zone 2, or general endurance pace.
For Weight Loss: The key to weight loss is creating a caloric deficit. The most effective exercise is that which contributes most to this deficit in a sustainable way. Focusing on total energy expenditure is far more important than the substrate used during the workout itself.
Ultimately, there are no shortcuts. The proven principles of progressive overload, consistent training volume, and managing overall energy balance remain the cornerstones of improving endurance performance and achieving a healthy body composition.