Original episode & show notes | Raw transcript
For years, the cycling world has been dominated by a simple, memorable definition: Functional Threshold Power (FTP) is the highest power you can sustain for one hour. The podcast correctly points out that this is a persistent oversimplification that can hinder effective training.
The Origin: The idea originates from Dr. Andy Coggan and Hunter Allen’s seminal book, Training and Racing with a Power Meter. However, the book itself offers slightly conflicting definitions:
One definition describes FTP as the power a rider can maintain in a “quasi-steady state for approximately one hour.”
Another suggests a one-hour time trial is the most direct way to measure it.
The Physiological Reality: The more accurate and useful definition is physiological. FTP represents the upper limit of a sustainable aerobic effort. It’s an inflection point in metabolic dynamics.
Below FTP: You can clear lactate at the same rate you produce it. Fatigue accumulates slowly.
Above FTP: Lactate production outpaces clearance, leading to a rapid cascade of metabolic changes that cause fatigue to accumulate much more quickly.
This is where Time to Exhaustion (TTE) becomes the critical, individualized variable. TTE is simply how long you, as an individual, can sustain your FTP. For most trained cyclists, as the podcast notes from experience, this is typically between 35 and 50 minutes, not a full 60.
The podcast centers its argument on a key paper: “Training Effect on Performance, Substrate Balance, and Blood Lactate Concentration at the Maximal Lactate Steady State in Master Endurance Runners” by Veronique Bilat and her colleagues.
This study provides a powerful illustration of how to effectively train your threshold.
The Setup:
Subjects: Well-trained masters runners who, importantly, had a long history of only doing long, slow distance runs. They had a strong aerobic base but were “naive” to structured, high-intensity intervals.
The Metric: They measured Maximal Lactate Steady State (MLSS), which is the physiological equivalent of FTP. For runners, this is a velocity (speed), whereas for cyclists, it’s a power output.
The Intervention: The runners underwent a 6-week training block consisting of two weekly interval sessions performed at their MLSS/FTP. The key was the progression: they didn’t increase the intensity (speed); they increased the duration of the intervals. This is what the podcast calls “extensive threshold work.”
The results of the Bilat study reveal the true nature of threshold adaptation.
The runners’ average TTE at their FTP pace increased from ~45 minutes to ~63 minutes. This is the central lesson: Training at your threshold primarily extends the duration you can sustain that power.
The runners’ actual FTP (as a percentage of their VO2 max) remained stable. This is counterintuitive for many athletes who believe “FTP workouts” should always make their FTP number go up. In well-trained individuals, the first and most significant adaptation is becoming more durable and efficient at their current threshold.
This is where it gets interesting. Why did their TTE increase so much?
Improved Lactate Dynamics: The study found a strong correlation: the lower an athlete’s blood lactate was in the first 10 minutes of the effort, the longer their final TTE was. This doesn’t just mean they produced less lactate; it means they became vastly better at oxidizing (using) lactate as a fuel source within the working muscles. Better lactate clearance means less metabolic disruption, sparing other fuel sources and delaying fatigue.
Improved Fuel Utilization (Substrate Balance): The study also showed that the athletes with the longest TTE were burning less carbohydrate and more fat at their FTP. This is a hallmark of elite metabolic fitness. By improving their ability to use fat for fuel at a very high intensity, they spared their finite muscle glycogen stores. Since glycogen depletion is a primary cause of fatigue in long-duration events, this adaptation directly translates to a longer TTE.
These adaptations—more mitochondria, greater capillary density, enhanced enzyme activity—are the “engine room” changes that make an athlete more robust.
The podcast translates this science into actionable training principles.
Prioritize “Going Long” Over “Going Harder”: For your threshold work, the primary goal should be to progressively increase your total time-in-zone. If you can do 2x20 minutes at FTP, your next goal shouldn’t necessarily be 2x20 at 5 watts higher. It should be 3x15, then 2x25, then eventually 60-75 minutes of total work in a session.
The Power of Volume: The runners in the study already had a high volume of endurance training. This is critical. Long, steady endurance rides (Zone 2) drive many of the same adaptations as extensive threshold work (e.g., mitochondrial growth, fat oxidation). High volume provides the aerobic foundation that makes your threshold work so effective.
When to “Raise the Roof”: Once your TTE is well-developed (the podcast suggests > 55-60 minutes), your body is primed to benefit from VO2 max training. You have built a massive aerobic engine that can now support a higher ceiling. Pushing up your VO2 max at this point is more likely to pull your FTP up with it.
TTE is the Real-World Performance Metric: A longer TTE doesn’t just help in a 40km time trial. In a road race or criterium, every surge above threshold creates a metabolic “debt.” An athlete with a longer TTE has a more efficient engine to clear that debt and recover between efforts. They are simply more fatigue-resistant and have more “depth” late in a race.
In summary, the podcast champions a shift in thinking away from a singular focus on the FTP number and towards developing metabolic fitness and durability. The most direct path to this is through extensive threshold training, supported by a solid foundation of endurance volume. By extending your TTE, you are fundamentally becoming a more efficient and robust athlete.