Original episode & show notes | Raw transcript
This document provides a detailed breakdown of the core concepts discussed in the Empirical Cycling podcast episode concerning Functional Threshold Power (FTP) and Time to Exhaustion (TTE). The podcast argues that viewing these two metrics as opposing forces is a fundamental misunderstanding of endurance physiology and effective training. Instead, they are two critical dimensions of a single concept: an athlete’s sustainable aerobic performance.
To understand the discussion, we must first move beyond simplistic definitions.
The podcast defines FTP not as a simple number derived from a short test, but as a performance threshold or fatigue threshold. This is a critical distinction.
Below FTP: An athlete’s body can clear metabolic byproducts at a rate equal to or greater than their production. Fatigue accumulates very slowly, and effort can be sustained for a long time.
Above FTP: The rate of metabolic byproduct accumulation exceeds the body’s ability to clear it. Fatigue accumulates much more rapidly, leading to a comparatively quick failure.
This definition treats FTP as a physiological boundary that governs the nature of fatigue, rather than just a number to be maximized.
TTE is defined simply as the maximum duration an athlete can sustain their FTP.
If an athlete’s FTP is 300 watts, and they can hold exactly 300 watts for a maximum of 45 minutes, their TTE is 45 minutes. This introduces the crucial second dimension to threshold performance: duration. Thinking of FTP as just a power number (e.g., “My FTP is 300 watts”) is one-dimensional. A two-dimensional understanding is “My FTP is 300 watts with a TTE of 45 minutes.”
The central thesis of the podcast is that the “debate” over whether to train for a higher FTP or a longer TTE is a “kayfabe” — a manufactured conflict. The perception of a conflict arises from an outdated, one-dimensional view of training where the only goal is to increase the FTP number.
A holistic and effective training program does not choose one over the other; it seeks to improve both. The prioritization and timing of training blocks to address each metric is the art of coaching and long-term planning.
For any athlete past the initial “newbie gains” phase, raising FTP is extremely difficult. The podcast emphasizes this point:
Marginal Gains: A 5-15 watt increase in a year for a well-trained amateur is a solid result. A 20-watt gain is “ecstatic,” and 30 watts is exceptional, even for professionals.
The Limiter is Recovery: The primary barrier to raising FTP is not the training itself, but the body’s ability to recover from the intense stimulus required.
High-Intensity Stimulus: Raising the FTP ceiling often requires very demanding training, such as VO2 max intervals.
A common argument for focusing solely on FTP is that a higher FTP makes all sub-threshold intensities easier. If your FTP goes from 200W to 220W, your old FTP of 200W is now a sustainable “sweet spot” intensity.
The podcast acknowledges this is true, but with a major caveat: This strategy is only effective as long as raising FTP is relatively easy. For beginners, this effect is profound. However, for an experienced athlete who might spend a year fighting for a 10-watt gain, the “rising tide” is more of a slow trickle. Relying solely on this mechanism for endurance improvements yields diminishing returns.
Constantly training to raise FTP is described as “fucking hard.” The immense fatigue it generates can:
Compromise other training: There is little energy left for skill work, sprinting, strength training, or simply enjoying rides.
Hinder Race-Specific Preparation: An athlete might show up to a race with a high FTP but be too fatigued to express it, or lack the specific skills and repeatability needed for the event.
Training to increase the duration you can hold your FTP is presented as a powerful, and often overlooked, training modality.
Faster, Easier Improvement: Unlike the slow grind of raising FTP, TTE can be progressively improved in nearly every session (e.g., extending intervals from 2x20 min to 2x22 min).
Lower Systemic Fatigue: While still challenging, TTE-focused workouts (like long sweet spot or threshold intervals) are less systemically taxing than VO2 max sessions, allowing for better recovery and consistency.
Directly Builds Fatigue Resistance: This is the most direct way to improve endurance. The ability to resist fatigue is more valuable in long races (road, gravel, fondos) than an extra 10 watts of FTP that you can only hold for 30 minutes.
Serves as an Objective Fatigue Gauge: The inability to hit your target interval duration is a clear, objective sign that you are under-recovered and need to adjust. It removes guesswork.
Focusing exclusively on TTE can create a “diesel engine”—an athlete who can go at one steady pace for a very long time but lacks the ability to surge, attack, or handle the sharp accelerations common in racing. If a race demands an effort significantly above your current FTP, a massive TTE will not help you make the selection. You must also raise the ceiling (FTP), not just extend how long you can press against it.
The podcast advocates for a long-term approach where FTP and TTE are developed in concert. A common and effective strategy is:
Build the Base: Focus on extending TTE to build a deep foundation of fatigue resistance.
Raise the Ceiling: Use that robust aerobic base to handle a demanding block of high-intensity training (like VO2 max work) to raise FTP.
Consolidate: Return to TTE-focused work at the new, higher FTP to “lock in” the gains and make that new power level sustainable for longer durations.
This cyclical approach is fundamental to long-term athletic development.
The podcast is critical of predictive, short-form FTP tests (e.g., ramp tests, 8-minute or 20-minute tests) because:
They are heavily influenced by an athlete’s anaerobic capacity, which may not reflect their sustainable aerobic power.
The relationship between the test result and actual FTP is not static; it changes as an athlete’s fitness profile changes.
The preferred method is a long-form FTP test, which is in itself a TTE test. By having an athlete ride at their perceived FTP for as long as possible (e.g., 35-60+ minutes), you directly measure both the power (FTP) and the duration (TTE). The guiding principle is that the best measure of performance is performance itself.
The debate between FTP and TTE is a false dichotomy. They are not competing metrics but two inseparable components of an athlete’s aerobic capability.
FTP represents the intensity ceiling of sustainable aerobic effort.
TTE represents the durability at that ceiling.
An effective, individualized training plan understands the athlete’s specific needs, their event demands, and their unique physiology. It uses periods of focused training to push up the ceiling (FTP) and other periods to extend the foundation (TTE), ultimately building a more capable and resilient athlete who can perform better in the real world, not just in a test protocol.