FTP – 80/20 Endurance

The concept of a limiting rate of oxygen consumption during exercise, or VO₂max, has existed since 1923. For almost a century, we’ve known that oxygen consumption increases as the intensity of exercise increases, that some people are able to consume oxygen at a higher peak rate than others, and are therefore able to exercise more intensely, and that training increases an individual’s highest achievable rate of oxygen consumption, and with it their exercise capacity. No other phenomenon has been as exhaustively in exercise science. Just now I performed a keyword search of “VO₂max” on PubMed and got 11,752 hits.

You might think that by this point there would be nothing left to learn about the phenomenon. But if you did, you’d be wrong! Two new studies touching on VO₂max have been published within the past few weeks alone. I’d like to tell you about one them here, as it offers practical lessons for everyday endurance athletes like us.

Cyclists and triathletes often use a 20-minute time trial to estimate their functional threshold power (FTP), which is the highest wattage an athlete can sustain for 60 minutes. Obviously, no athlete can sustain quite as much power for 60 minutes as they can for 20 minutes, so a simple formula is used to estimate 60-minute power from the result of a 20-minute test. All the athlete has to do is multiply their average wattage in the test by 0.95. For example, if you average 226 watts in your 20-minute time trial, your estimated FTP is 206 x 0.95 = 215 watts.

This one-size-fits-all formula is based on the assumption that athletes are able to sustain 5 percent less power for 20 minutes than they can for 60 minutes. But does this formula really fit all athletes? That’s the question Sebastian Sitko of the University of Zaragoza and colleagues sought to answer in a study published recently in the Journal of Science and Medicine in Sport.

Eighty-seven cyclists representing a range of abilities were statistically separated into four groups: recreationally trained (average VO₂max 46.9 ml/min/kg), trained (average VO₂max 59.5 ml/min/kg), well trained (average VO₂max 66.4 ml/min/kg), and professional (average VO₂max 74.3 ml/min/kg). All of the subjects completed a 20-minute time trial that was used to estimate each individual’s FTP through the aforementioned formula. Subsequently, they performed a second test that required them to pedal at their estimated FTP as long as possible.

Here are the results: On average, the recreationally trained cyclists were able to sustain their estimated FTP for 35 minutes, while the trained cyclists lasted 42 minutes, the well-trained cyclists 47 minutes, and the professional cyclists 51 minutes. As we see, the Allen & Coggan test (as it is known) tends to overestimate FTP, and the lower your VO₂max is, the greater the error is likely to be. The reason is that the rate of decline in sustainable power over time is steeper for less aerobically fit athletes, who are less fatigue resistant.

This becomes a problem for athletes who base their training zones on the one-size-fits-all formula proposed by Allen & Coggan. An athlete with a VO₂max of 47 who uses 95 percent of 20-minute power as their FTP will probably end up with zones that are too aggressive and will consequently train too intensely. This doesn’t mean we have to dispense with the protocol altogether; it just means that athletes of different levels need to use different multipliers to generate an accurate estimate of FTP from the result of a 20-minute time trial.

My suggestion is to use the same result to calculate your power-to-weight ratio, which is a decent proxy for VO₂max, hence a good way to determine your level as a cyclist and select an appropriate multiplier for estimating FTP. Simply divide your 20-minute power by your weight in kilograms, see where this puts you on the table below, and use the recommended multiplier to calculate your FTP.

	Power-to-Weight Ratio
Men	<2.9 W/kg	2.9-3.8 W/kg	3.9-4.8 W/kg	>4.8 W/kg
Women	<2.1 W/kg	2.1-3.0 W/kg	3.1-4.0 W/kg	>4.0 W/kg
Multiplier	0.92	0.93	0.94	0.95

Let’s go back to our earlier example of an athlete who averages 226 watts in a 20-minute time trial. Now let’s suppose this athlete weighs 73 kg (160.6 lbs), which gives them a power-to-weight ratio of 3.1 W/kg, and let’s also suppose the athlete is male. Referencing our handy-dandy table, we see that the appropriate multiplier for estimating FTP is 0.93, which yields a result of 210 watts. That’s a number the athlete is more likely to be able to sustain for a full hour than the 215 watts we got from the Allen & Coggan formula and will generate power zones that better fit the athlete. Now you try!

Recently I created a custom training plan for an Italian ultraendurance cyclist who was preparing for a pair of multiday, multi-thousand-kilometer bike tours, and who told me in the onboarding questionnaire he submitted that increasing his functional threshold power (FTP) had been a major point of emphasis in his training.

For the runners in the room, FTP is intended to serve as a proxy marker of lactate threshold intensity on the bike. It is, by definition, the highest power output a cyclist can sustain for one hour (this being the average amount of time a trained cyclist can sustain lactate threshold intensity in a laboratory setting) and is determined through a 20-minute time trial, where the average wattage sustained in this test is multiplied by 0.95 to arrive at a final result.

Again for the runners in the room, an FTP test is essentially the equivalent of a 5K running time trial, which takes 20 minutes to complete, give or take. So, tell me: If you were training for a seven-day running event that would cover many hundreds of miles in total, how concerned would you be about lowering your 5K time?

It’s not that FTP is completely irrelevant to the kind of fitness needed to excel in a multiday event. It’s just that other things are more relevant, and therefore treating FTP increase as a point of emphasis amounts to taking your eye of the ball. But I’ll go even further and say that obsessing over FTP increase is a counterproductive distraction if you’re training for anything other than an FTP test. In fact, even if you are training for an FTP test, increasing your FTP should not be your top priority throughout the process.

That FTP has become the standard measure of cycling fitness is more a matter of historical accident and exigency than any intrinsic superiority of FTP relative to other measures. Research has shown that various tests and measures, including ventilatory threshold, respiratory compensation point, respiratory exchange ratio, maximal lactate steady state, maximum power in a graded exercise test, power-to-weight ratio, and VO₂max are about as good at predicting real-world cycling performance. The only reason FTP rather than any of these other things is the bright, shiny object that cyclists and triathletes can’t seem to take their eyes off is that the other things aren’t as practical outside of the exercise lab.

The same principle holds for any test or metric you might use to measure fitness or a component thereof in the training process. Among athletes there is an unfortunate propensity to seek continuous improvement in any test or measurement you put in front of them, no matter how tangential it is to the specific type of fitness they need in order to excel on race day. I’ve seen athletes sabotage their own progress by overemphasizing everything from VO₂max to body weight to barbell squat performance.

I get it. If a given metric is performance-relevant, it’s easy to assume that improving that metric will always translate to better performance on the race course. But it doesn’t work that way, because there’s no such thing as general fitness. Each event demands a very specific type of fitness, and the goal of training is to be good at that, not good at every conceivable proxy. For example, if your VO₂max is increasing in the late stages of training for an ultramarathon, it’s likely because you’re not doing the necessary training to increase your respiratory exchange ratio, which has greater relevance to ultramarathon performance.

The time to see your VO₂max increasing in training for any event that is likely to take more than an hour to complete is early in the process, before you shift your focus to more race-specific fitness priorities. In fact, if you’re a more experienced athlete, you could successfully gain in the type of fitness you really need for a particular event without seeing any change in your aerobic capacity. The typical elite endurance athlete attains a lifetime peak in VO₂max in their early 20s, and then continues to improve on the race course for another decade. Kellyn Taylor, my former honorary teammate on HOKA Northern Arizona Elite, recently set a 10,000m PR of 31:07 at age 34. It’s very likely her VO₂max was higher at 24.

There are some things you might measure in the training process that, in some cases, should decline in the late stages of preparing for a race. Examples:

If your sit-and-reach performance (i.e., hamstrings flexibility) declines ahead of any running race, that loss of flexibility indicates that your “leg stiffness” is increasing and your running economy improving, which is a good thing.
A 2004 study by researchers at Ball State University found that the calf muscles of college cross country runners got weaker and smaller over the course of a competitive season, which sounds bad, but the muscles actually shrank more than they weakened, which means they actually got stronger relative to their size, which is a good thing for a distance runner.
Similarly, when I was training for Ironman Santa Rosa in 2019, my anaerobic capacity decreased in parallel with gains I made in aerobic fitness and endurance, which was good for my Ironman performance prospects.

It is useful and all but unavoidable to measure things during the training process. But it’s important to maintain perspective on the numbers as you go. The goal is not to get better at everything all the time. The goal is to maximize race-specific fitness on race day. Achieving this goal will require that you prioritize different components of fitness in the proper order and that you hold steady in certain metrics and be content to go backward in certain others in some periods. In short, govern the metrics, don’t let the metrics govern you.

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