Every triathlete has done it. You warm up, hammer a 20-minute effort, multiply by 0.95, and call it your FTP. You plug that number into your training software, and it spits out five colour-coded zones. Job done.
Except it is not done. Not even close. That single number is telling you far less about your physiology than you think, and it is probably steering your training in the wrong direction.
What an FTP Test Actually Tells You
A 20-minute FTP test tells you how well you can sustain a 20-minute effort. That is it. It provides one data point at one duration, and then applies a coefficient to estimate a threshold value. The problem is that this number represents a performance metric, not a physiological one. It tells you what you did. It does not tell you how your body produced the energy to do it.
Think of it this way. Two athletes could test at identical FTP values and have completely different physiological profiles underneath. One might have a massive aerobic base with a low ceiling. The other might be glycolytically dominant with a narrow aerobic zone. Prescribing the same training zones to both athletes based on the same FTP number would be a mistake, because they need fundamentally different training to improve.
The Problem With One Number
The core issue with any single-threshold approach is that it is impossible to build a truly individualised program from one number. You cannot determine where an athlete's aerobic threshold sits. You cannot see the gap between their first and second thresholds. You cannot classify whether they need to build their aerobic base or raise their ceiling. All of those insights require at least two anchor points.
This is why the Tremayne Performance system uses two thresholds, not one. By identifying both HRVT1 (the aerobic threshold, where DFA Alpha1 crosses 0.75) and HRVT2 (the anaerobic threshold, where it crosses 0.50), we get a complete picture of the athlete's metabolic profile. Two thresholds. Three zones. A genuine physiological map.
Why Two Thresholds Change Everything
Once you have two threshold values, the gap between them becomes a profiling tool. That gap tells you which energy systems dominate, where the athlete has capacity to develop, and what kind of training will produce the biggest return on investment.
An athlete with a narrow gap between HRVT1 and HRVT2 and a low first threshold has a compressed aerobic zone. They are glycolytically dominant. They need extensive sub-threshold work to build their aerobic engine. Prescribing them lots of VO2max intervals based on an FTP number would be the worst possible approach.
An athlete with a wide gap and a high first threshold has the opposite profile. Their aerobic system is well developed, but their ceiling is low. They need targeted high-intensity work to expand their capacity above the second threshold.
You simply cannot see any of this from a single FTP test. The number might be identical for both athletes, but the training they need is completely different.
What About Critical Power?
If you are going to use a single-threshold approach, critical power or critical velocity testing is far more applicable than a standard 20-minute FTP test. These methods use multiple data points across different durations to build a power-duration or speed-duration curve, which provides a much richer performance profile.
However, even critical power gives you a performance profile rather than a physiological one. It tells you what you can sustain across various durations. It does not tell you how your body produces the energy to sustain it. For that, you need to measure the thresholds directly.
How DFA Alpha1 Testing Works
DFA Alpha1 analysis measures heart rate variability during a structured ramp test. As intensity increases, the fractal correlation properties of your heartbeat change in predictable ways. The first breakpoint (0.75 crossing) closely correlates with the first ventilatory threshold. The second breakpoint (0.50 crossing) correlates with the second ventilatory threshold.
From a single ramp test, performed in your own training environment with a compatible heart rate monitor, you get both thresholds identified non-invasively. No lab required. No blood lactate. No gas exchange mask. Just your trainer, your heart rate strap, and a structured protocol.
The result is a genuine physiological profile that tells you not just how fit you are, but what kind of fit you are, and exactly how your training should be structured to keep improving. If you are new to physiological data, heart rate training is a practical place to start. And if you suspect your current zones are off, here is how to tell whether your training zones are actually right, and why your creeping heart rate on long sessions is usually a zone problem, not a fitness problem.
Two athletes with the same FTP can need completely different training. You will never know which one you are from a 20-minute test.