Power isn’t everything~The ability to sustain it wins the race.
Most athletes train to raise their FTP. The athletes who race well late train to hold it — on the bike and on the run. Here’s the metric that separates them, and the sessions that close the gap.
Raise the FTP. Hit the watt target. Chase the number on the screen.
It’s how most power-based training works — and it makes sense. Threshold power is the physiological anchor of nearly every training system in use today. A higher FTP means more speed at the same effort. That matters.
But there’s a second question that most training programs don’t ask loudly enough:
"How long can you actually hold that power?"-The question that separates training fitness from race fitness
That question sits at the center of what separates athletes who look fast in training from athletes who race fast — especially in triathlon, where the bike and run don’t exist in isolation. They exist in sequence, and fatigue compounds with every mile.
Two athletes, same FTP — very different races
Consider two athletes preparing for a 70.3. Both test at 240 watts on the bike. On paper, they’re equivalent.
On race day, one rides at 88% of threshold for 2:20 and still runs off the bike with controlled, consistent power. The other starts fading at 90 minutes, limps through the final 20 miles, and runs what can generously be called a survival shuffle.
Same FTP. Completely different race.
The difference isn’t the number at the top of the power-duration curve. It’s the shape of the curve below it — how long each athlete can sustain power at or near threshold before the physiological wheels come off.
That quality has a name: Time to Exhaustion (TTE). And it is one of the most underutilized metrics in age-group triathlon coaching.
What is Time to Exhaustion?
TTE was formally introduced to the coaching world through Dr. Andrew Coggan’s work in WKO5. The definition is precise: the maximum duration for which a power equal to model-derived FTP can be maintained.
On the power-duration curve, TTE appears as a visible “kink” — the point where the curve begins its downward turn after a sustained plateau. Up to TTE, you’re in a quasi-steady state. Beyond it, the body’s ability to match ATP demand aerobically starts to fail, and power output progressively declines.
For many trained athletes, TTE falls between 40 and 55 minutes. It can range from 30 minutes in less-developed athletes to 70 minutes in highly trained long-course specialists. More importantly — TTE is trainable.
Recreational
Trained
Well-trained
Professional
Median TTE at functional threshold power by performance level · Muñoz-Pérez et al., Journal of Science and Medicine in Sport, 2022
Research Finding
TTE increased significantly with both experience and performance level — meaning it responds to training. A recreational cyclist with a 35-minute TTE and a professional with 51 minutes may have similar FTPs. The professional can simply sustain that power for 45% longer before the curve breaks down.
Muñoz-Pérez et al. (2022), Journal of Science and Medicine in SportHow coaches use TTE — two levers, not one
In WKO5, the power-duration model gives coaches two distinct programming levers:
"If an athlete's FTP is adequate but TTE is short, the training priority isn't more threshold intervals — it's structured work that extends duration at threshold-level stress."-The coaching decision that most programs miss
The run side of the equation
Power-based analysis on the bike has been standard for two decades. On the run, it’s newer territory — but with tools like Stryd, the same framework now applies.
Stryd defines a running threshold called Critical Power (CP), and TTE logic holds exactly: an athlete’s ability to hold run power near CP — especially after 90+ minutes of racing — determines whether the run split is a strength or a liability.
For triathletes, this is even more consequential. The run doesn’t happen fresh. It happens after an open-water swim and a 1.2 to 112-mile bike. The physiological cost of that bike creates pre-accumulated fatigue that makes run power sustainability the central challenge of the discipline.
Coaches call this run durability or fatigue resistance. A general starting target for 70.3 run power is approximately 87–90% of running CP — but that target only holds if the athlete has trained the TTE and durability to sustain it.
"The run doesn't happen fresh. It happens after an open-water swim and a 56 to 112-mile bike. Fatigue is already in the account."-Why run durability training is different in triathlon
Total: 40 min structured work
48 total minutes at threshold intensity
The triathlon context — putting it together
In triathlon, the relationship between bike TTE and run durability is direct — and consistently underestimated.
An athlete who rides at 85% of FTP for 2.5 hours but has a TTE of only 40 minutes is spending the final hour of the bike in a physiological state they have not trained to manage. The legs arrive at T2 with a biochemical debt that no amount of run fitness can fully offset.
Build TTE on the bike first. Then train the run to operate from accumulated fatigue.
Brick sessions are not just transition practice — they are the primary mechanism for building run durability in a triathlon-specific context. The athlete who can hold 90% of running CP for 45 minutes after a 2-hour bike at 80–85% FTP has built something that a fresh-legs tempo run simply cannot replicate.
"Most athletes train hard. Few train right. The athletes who race well late are athletes whose training has specifically targeted the ability to sustain power over time."Catalyst Endurance Coaching
Four things to act on this week
- Know your TTE If you train with WKO5, it's already modeled from your power-duration curve. Most trained athletes fall between 40–55 minutes. If you don't know yours, that's the first gap to close.
- Check both levers, not one When you review your fitness trend, look at FTP and TTE together. A stagnant FTP with a lengthening TTE is real, raceable fitness progress — and it translates directly to your next race.
- Shift duration at threshold, not just intensity As your target event approaches, interval duration should increase and rest should shorten — shifting the emphasis from power development to power sustainability.
- Build brick durability with intent Run durability done fresh is only half the work. The other half happens off the bike, in a controlled fatigued state, at specific run power targets.
Work with Catalyst Endurance
Ready to train the metrics that matter on race day?
Knowing your FTP is a start. Knowing your TTE — and having a plan to extend it — is where race performance is actually built. If you want that analysis applied to your data and your season, let's talk.
References
1. Coggan, A.R. & Cusick, T. (2016). Introduction to the Time to Exhaustion (TTE) Metric in WKO5. TrainingPeaks / WKO5 Knowledge Base. wko5.zendesk.com
2. Muñoz-Pérez, I., et al. (2022). Time to exhaustion at estimated functional threshold power in road cyclists of different performance levels. Journal of Science and Medicine in Sport, 25(9). https://doi.org/10.1016/j.jsams.2022.06.009
3. Blondel, N., et al. (2020). Time to exhaustion during cycling is not well predicted by critical power calculations. Applied Physiology, Nutrition, and Metabolism. PMID: 31935109
4. Salam, H., Marcora, S.M. & Hopker, J.G. (2018). The effect of mental fatigue on critical power during cycling exercise. European Journal of Applied Physiology, 118(1). PMCID: PMC5754415
5. Stryd. (2025). Top Stryd Training Sessions of 2025. blog.stryd.com
6. Coggan, A.R. (2022). Stamina — resistance to fatigue during prolonged exercise. WKO5 Knowledge Base. wko5.zendesk.com