The Real Problem With FatMax (It's Not About Carbs vs Fat)

The real problem with FatMax isn't about carbs versus fat—it's that the test is fundamentally unreliable. Michael Eriksson, host of *That Triathlon Show*, dismantles the myth that tracking FatMax intensity is valuable for triathletes, revealing that its coefficient of variation (CV) is often 10% or higher, meaning any change below 28% is likely just noise. This makes it impossible to trust individual test results, even if you're training hard. The episode pivots from physiology to statistics, introducing the 'smallest detectable change' (SDC)—a simple formula (CV × 2.77)—that reveals how much a metric must change to be real, not random. Using this, Eriksson shows that even FTP testing, often seen as gold standard, becomes useless if its CV is 10% instead of 1%. The takeaway? Most performance markers—like HRV, blood lactate, and running economy—are too noisy to track individually. The solution? Average multiple measurements or accept that some tests are only useful for research, not personal training. Finally, he debunks the idea that burning more fat at race pace improves performance, explaining that carbohydrates yield 7% more energy per liter of oxygen, making fat oxidation a performance limiter, not an advantage. For most triathletes, fueling with carbs is smarter than chasing fat-burning efficiency.