Why Durability Matters More Than FTP in Triathlon Training — Triathlete

It is the final proof that your training has been successful, and year after year, triathletes work hard to see if they can improve their functional threshold power, or FTP. We test, and we retest, and we become totally obsessed with that 20-minute power figure. A high FTP gives you race readiness, writ large.

Then race day actually arrives.

Two hours into a 70.3 bike leg, or halfway through an Ironman, the watts fall apart and heart rate spikes as pacing goes to hell. All of a sudden, that big number on TrainingPeaks that you thought looked so good is not what you can hold in the race.

That disconnect reveals a hard truth many long-course athletes fail to recognize: peak-power numbers do not determine endurance-race victories. Durability does.

What is durability, really?

In endurance sports, muscular endurance is your capacity to sustain performance despite the accumulation of fatigue. It’s not the number you can dump when your legs are fresh; it’s how much power you can keep pumping out when you’re three hours deep in the pain cave.

As the race drags on, this drop-off is a fraction of others. Their heart rate stays steady no matter what work they are doing. Their pacing gets recorded in their brain, helping them remain efficient without quickly exhausting their energy. In simple terms, durability means resisting physiological drift, which is the slow decline that makes athletes perform worse over time.

You’ll hear this all the time in trail and ultrarunning communities – that they know the winner is otherwise just the person who slows down least. Whereas in triathlon, we track peak metrics (FTP). Those numbers reflect our potential, but they don’t tell us what happens three hours into a race.

In a training scenario, two athletes may test with identical threshold power. But the third hour of race day, the durable athlete is still spinning high and happy at 75-80% their threshold while their less durable counterpart is seeing their watts fall through the floor. That’s everything in long-course racing.

The FTP testing trap

We can accomplish this by examining the default 20-minute test. You pedal like hell for 20 minutes, multiply by 0.95, and voilà! There’s an approximation of your lactate threshold.

The metric is not the issue. Our use of it is.

Anyone with a decent anaerobic engine has FTP numbers struck on very short testing protocols. And while you may be able to grind out some gigantic 20-minute number, that does not mean that you have the deep aerobic strength required to hold those numbers for the duration of a long-course event. You are doing this at a peak level, not in an effort stretched out under extreme fatigue.

The inflated, seemingly “fresh” number serves as a basis for setting your race goals – but it’s often unrealistic for your actual physiology. The first hour feels great. The second hour gets uncomfortable. In hour three, your power is dwindling, and your heart rate is red-lined. You didn’t suddenly lose your fitness; that dream race of yours was a pipe dream in the first place.

The seasonal FTP illusion

FTP is also perilous because it’s so easy to game early in the season. Then you can add some intensity, throw in a few threshold intervals, and that 20-minute power number will often go up within a matter of weeks. You feel smarter, the data is sexy, and you believe you’ve nailed it.

But simply raising your ceiling doesn’t raise your foundation.

Your FTP can go from 215 to 230 watts in spring – yet all you’ve done is improved your race execution if you still can’t hold steady power for three hours by late summer. You’ve just assembled something that sounds like progress, but it doesn’t have the cash. For long-course athletes, your durability dictates how much of that threshold power you ultimately use late in the race.

The real name of the game is fatigue resistance

At its heart, long-course triathlon is always a game of fatigue management. Every single one of those athletes standing on the podium doesn’t necessarily have the highest FTP; they’re just able to make that happen with less physiological stress.

To create real endurance, you must address the following four cornerstones:

1. Aerobic power: A powerful aerobic engine can produce the power you need for your goal race without causing metabolic distress.
2. Fueling: You need to consume carbohydrates regularly. To delay fatigue, maintaining energy availability is essential and keeps your tank from running empty. For more on carbohydrates and race-day fueling, check out The Triathlete’s Guide to Race Fueling for Every Distance.
3. Muscle durability: Your muscles must be physically conditioned to continue contracting forcefully for many hours of repetitive motion. You develop this with big-gear bike work, off-the-bike transition runs, and target-heavy strength training.
4. Pacing: We’ve said it before, and we’ll say it again: Going out hard, even for a few seconds, will drain you faster and ruin your endurance by the end of the day.

If your endurance is sufficiently dialed, your heart rate and perceived exertion will correspond closely to your power output. And when that’s not the case, you experience cardiovascular drift – your exertion goes up, but your power drops off.

How to stop guessing and measure your triathlon durability

Durability isn’t one magical number; it’s a trend that you should discover in your historical data.

First, mind your decoupling. Power-to-heart-rate decoupling quantifies how much your heart rate “drifts” upward compared with power as time passes. The takeaway is, if your decoupling was low on a three-hour steady effort, you are doing an amazing job of controlling the workload aerobically.

Next, stop fixating on your 20-minute bests. Look at your long intervals. Are you able to consistently hit your target watts from ride hours two through four?

Finally, track your heart rate trends using a heart rate monitor. If your power is consistent, but your heart rate has slowly risen toward the stratosphere, then your body is really working to maintain that output. Your durability still needs work.

These trends will tell you far more about how ready you are for the race than any maximal test ever can.

Setting your triathlon race power accurately

Fill the gaps left in your 70.3 or Ironman plans with rigid FTP percentages. So you’re not talking about your long training sessions.

Longer 60- to 90-minute sessions at race speed will expose everything. Can you hold it still without your heart rate roaming? Are you getting 80 to 100 grams of carbohydrate per hour so the gas tank doesn’t go empty?

Race sims are your last step into reality. Additionally, they inform you that your actual sustainable race power is almost always lower than what the FTP numbers were showing you, but it is far more repeatable on race day when it counts.

The athlete who clings on for dear life wins

It’s common to see athletes start strong but struggle later in long-course races. The issue is that your peak performance might not be sufficient to secure a win. Success is achieved – and expended – during the slow, grueling effort that unfolds over several hours.

The small pacing error in hour one builds into an increased heart rate, a nutrition bottleneck, followed by collapsing numbers. In the final hour of the bike, this T1 superhero is simply hanging on and doing everything she can to keep turning over those pedals.

The durable triathlete, meanwhile, runs well within themselves. Their power is steady, their heart rate well-regulated, and they are setting themselves up to actually run the run.

The difference between the two athletes is not, ultimately, their FTP. It’s their durability. The triathlete who fades the least on course is the one who takes it all.