How Many Watts Can You Hold?

How to Use a Power Meter in Triathlon and Cycling

First of all, what’s a power meter? First appearing as far back as the 1980s and 1990s, power meters brought to cycling what rowers had known for decades: measure the work that you’re doing, and you can quantify your training, setting clear goals and seeing if your work is paying off. For a population as data-centric as cycling, the power meter moved quickly from expensive and rare to ubiquitous. By measuring the strain that a cyclist puts into some part of the bike (the crank, spider, pedal spindle, or hub), a power meter tells the rider how much force per unit of time she generates. Instead of using heart rate, which lags behind the effort you are making, power measurement is real-time and direct: push harder on the pedals and you instantly see your output leap. You can then track how much power (measured in watts) you generate for different time intervals, and try to improve A) how many watts you generate for those units of time or B) how long those units of time are. Power meters provide excellent, usable data for any level of athlete.

Despite how commonplace they’ve become, however, they are rarely understood or used correctly by athletes or coaches. Most athletes who own power meters use them like thermometers, rather than the intricate pieces of medical equipment they can be. Athletes look at their power with a “what am I doing right now?” approach, in the same way you might check the weather to decide what you’re going to wear that day: immediate information, but no global or longitudinal perspective. Coupling a power meter with better understanding of the tool can give you the kind of perspective and accountability necessary for long-term development.

First of all, though, let’s give you some terminology you might need in this strange forest of watts and kilojoules.

• Functional Threshold Power, or FTP: you’ll hear this abbreviation a lot in triathlon and cycling circles, usually when a dude named Broheim says something like “Yeah, man, I tested my FTP back in April and it was, like, 330, but I think I was tired when I did it, so it’s probably a little higher.” OK, FTP is a number of watts you can hold for some theoretical length of time, usually between 40 and 70 minutes. Why theoretical? Well, Broheim from the example above has probably never actually held 330 watts for 40-70 minutes, but we’ll get into that later

• Watts: a unit of power, which is force divided time. Force is measured in Newton-meters, and time is measured in seconds, but we’re quickly getting off the garden path here. Think about a normal middle of the road 100w light bulb. If you ride at 100 watts, you can keep that light bulb lit as long as you keep pedaling.

• Kilojoule: a measure of work performed, roughly equal to a kilocalorie—it’s a great way to measure your total energy expenditure

So why is Broheim so concerned with his FTP? Well, once you know where your FTP sits, you can estimate your goal average power for different distances of races. Those averages are in the table below.

So let’s return to Broheim. If his FTP is actually 330 (which we kinda doubt) then here are the wattages he should be able to average during different distances of races.

Incredibly helpful, right? Now Broheim simply needs to do the work necessary to support his ability to ride at those wattages for the necessary amount of time for each race. Power meters do an excellent job of quantifying the output you have to hit, which in turn simplifies your training. In the past the only output figure we had was speed, which is a crude measure: things like wind, hills, and heat all play around with speed, but power is a direct measurement of your effort, which is under your control, whereas speed is not.

So this is all well and good, but why are we so skeptical about Broheim? Well, he probably arrived at his FTP of 330 by riding as hard as he could for 20 minutes and then taking 95% of that number. That’s not a terrible way to measure FTP, but there are better calculations these days. 95% of 20 minutes tends to over-estimate FTP, which means that Broheim’s numbers are too high for all his races! That’s a recipe for disaster. He’ll train beyond his abilities, and set his goals too high, and then underachieve at his race. Broheim doesn’t deserve that; for all his posturing, it sounds like he likes the sport. So let’s help him have the success he deserves.

Take 91% of 20 minutes

This method is pretty good, because it takes a familiar test and simply subtracts a larger number. In Broheim’s case, he tested at 347 for 20 minutes (since 330 is 95% of 347). In this new system, his FTP (the power he could hold for 40-70 minutes at maximum effort for that time) is 316, and his goal wattages are below:

Take 89% of 8 minutes

Another fine but not awesome method, and a good one for athletes that are new to the sport. Twenty minutes is a long time to ride as hard as possible, and many athletes get the pacing wrong, riding too hard and then blowing up and struggling to the finish, or staying wary of the effort and never going hard enough. Some caveats remain, however. Athletes who are exceptional at short intervals may end up with an inflated FTP using this method.

Take 100% of 60 minutes

Well, if you think athletes struggle with a twenty minute test, how well do you think they manage with a 60-minute test? This is a real toughie, and probably should only be used as a confirmation method with an athlete who is exceptional at pacing and is really into the suffering that sixty minutes riding as hard as she can go brings. Still, even though it’s hard to get right, this test comes with no strings attached: whatever you are able to do for one hour is your FTP (or, more accurately, your 60-minute critical power, but that’s another topic for another day).

Listen to Your Body (THE CAMPFIRE PREFERRED METHOD)

Kolie Moore at Empirical Cycling has a very good definition of FTP: “Above this number, you tire out faster. Below, you tire out slower.” Now, we know you type-A triathletes. You LOVE to have everything perfectly defined and spelled out. Guess what? Your physiology doesn’t operate under the same precision. Like a lot of stuff in anatomy, the difference between our idea of what’s going on and what’s actually going on is very different. If you’ve ever seen real human viscera, you know they are not nicely separated like the removable organs of that Transparent Man who stood at attention in your 8th grade Life Science class. So if you can learn the rough range of watts you can sustain for extended periods of time (like, 35+ minutes), and you know that you only have a small amount of time (like 3-5 minutes) above that range before you slow down, you have done a great job of finding your threshold. In terms of perceived exertion (RPE), threshold sits somewhere around “hard” but doesn’t cross over into “extremely hard.” At Campfire, we say that threshold is around 7-8/10, or “hard to very hard.” Once you’re in the 8-9/10 realm, we’d call that “extremely hard” and you can only hold that effort for a few minutes, not dozens of minutes. Do you want another one of Kolie’s methods that we have stolen? Check out this article he published that kinda launched him to coaching fame.

What do I do with it?

OK, you’ve done your test, and generated an FTP. Awesome! Nice work—those tests are never easy. Now, rather than bragging about it at the water cooler like Broheim (you’ll just confuse your co-workers, anyway—they’ll think you’re talking about a flower delivery service), use it to make your training better. Dr. Andrew Coggan’s power zones, established decades ago, still provide a good model for separating power zones into different training effects. Here they are, with Broheim’s more sensible FTP of 316.

You’ll note some asterisks in there, and here’s why. Without getting into some fairly hairy math and physiology, the important thing about these ranges is that they were intended, originally, to be DESCRIPTIVE, rather than PRESCRIPTIVE. Now what the heck does that mean? Well, good ol’ Doctor Coggan, who figured this stuff out, started with REAL athletes and real physiology, asking them to ride at different, controlled intensities, monitoring levels of blood lactate and other useful information, and then figured out the percentages from those studies. That means the the values we have are derived from ATHLETES THAT ARE NOT US, and we need to be careful of the fallacy of division, where we try to apply averages from a large population to a population of one. Really, for anything above FTP you’re best off going “as hard as you can go for the time prescribed.” So if your coach says “I want 4x5’ as hard as you can go,” you will figure out what that means through trial and error. Will your first intervals be perfect? No, but nothing is, Broheim! Don’t fret! Soon you’ll know what you can hold for certain time ranges, which is why we REALLY urge you to use the RPE column.

Great! Broheim’s got some training values, now. What he does with those are up to him, but here’s a very quick primer about training with power, and training in general.

1. Spend MOST (like, 55-65%) of your time in Z1, with time in ZR to recover from hard workouts. Yeah, you heard us: 80-90%. We’re not kidding. Endurance work makes you fast AND better at riding at any intensity at all. This is your bread and butter, so get after it. Also, try riding for four hours sitting between 55 and 75% of FTP and then come back here and tell me it was easy—you’ll be surprised.

2. Spend a fair amount of time (maybe 15-20%) of your time in Z3, progressing your training by adding time in zone each week.

3. Spend a (like 5%) of your time at HARD intensities, such as Z3 and all of Z4. There are some periods of the year when Z5 even makes sense for triathletes.

4. The remaining 10% of your time can be in the middle zones, like Z2 and low Z3. Spend more time here as you get close to your races.

There are many different ways to split your training intensities up (such as the 80/20 model), and remember that these values are simply averages for the population, so your actual zones may vary a bit. But without access to a physiology lab, it is difficult to pin them down precisely, and these zones will be sufficient to organize your training.

So have fun! Training with power is enjoyable, feels like a game, and allows you to see how you are improving. There are deeper ways to use these tools, but we hope you’ve taken away a sufficient introduction to the subject.