Functional Threshold Power (FTP) has been the standard to measure a myriad of metrics with, and the majority of the software utilized by athletes is reliant on this number being as accurate as possible.  Getting an accurate measurement is harder said than done however, especially if you are new to structured training.  The following article will serve to provide the more common ways to measure FTP, their pros and cons, and where the future of testing is headed (hint: it doesn’t involve much testing), in the author’s opinion.

Why FTP Anyways?

Functional threshold power (FTP) is the maximum power output an athlete can maintain in a quasi-steady state without fatiguing for 1 hour (1). Remember though, FTP is not the same as lactate threshold (LT).  FTP has been used by American coaches for years to track and prescribe workloads, and was first popularized by Andy Coggan, Joe Friel, Stephen McGregor, and Hunter Allen in their respective books and other contributions to the scientific literature.  Since FTP was cheap to test (free with a power meter), repeatable,  relatively accurate, and marketed well, it took over and is still widely utilized today.

A good analogy for FTP is to think of a car’s tachometer…

The red line represents your FTP.  You can push up to the red line and hold this output for approximately an hour (if your fitness is high, fatigue is low, and you are extremely motivated mentally), but push just a little bit over the red line and you run the risk of fatiguing early, and “blowing up” the car’s motor in this analogy.

Pitfalls with FTP + Deep Dive

Issue #1: Length of common testing protocols – In a little bit, we’ll get to the methods to test FTP.  You’ll notice that the most common ways are all less than a 1 hour testing effort, BUT your FTP is what you can hold for 1 hour without fatiguing.  This leads us to issue #2…

Issue #2: Athletes with high anaerobic capacity – Your FTP is a measure of how “strong” your aerobic (oxidative) system is.  To unpack that statement a bit more, aerobic capacity is how much energy you can produce via aerobic metabolism, how well you can combust lactate after a hard effort, and how economical (efficient) you are at a certain intensity, i.e. how good are you at doing the most work possible with the least amount of energy, both metabolic and mechanical, used.

*DEEP DIVE WARNING* Athletes with higher anaerobic capacities, i.e. increased energy being delivered via glycolysis, typically have a higher lactate tolerance and can push further “into the red” compared to their aerobically dominant counterparts.  Since FTP is an aerobic system measurement, these athletes’ tests can be overly inflated if the test is under 1 hour.  Why?  Here’s an example:

Joe Athlete has an FTP of 300w.  After doing a block of HIIT at Zones 5 + 6, his 20 minute FTP test improved by 30w and his FTP is now 315w.  He heads out to his local 40k TT, and uses his power meter to pin his output steady at 315w.  After 40 minutes, his output starts to drop dramatically and he winds up only being able to turn the gear over at 290w for the last 10k.

What happened in this example?  Joe’s last block improved his VLa Max (anaerobic capacity) which increased his glycolytic energy delivery rate to the working muscles, and subsequent mechanical force to the pedals, i.e. more watts.  However, the anaerobic system relies on carbohydrates, and especially stored glycogen, and has a finite amount of energy it can deliver compared to the aerobic system.  This increase in VLa Max made him feel like he was flying, until he exhausted his glycogen stores, and his aerobic system couldn’t keep up with the energy demands.  This, as we just read, lead to his power dropping dramatically and him finishing the race at 290w which is, in my opinion, a more accurate representation of his FTP.

Another way to look at this is the level of lactate accumulation in his system over the course of the 40k TT.  If his true FTP is closer to 290w, and he sets a pace of 315w he will accumulate (I am using arbitrary numbers here since I don’t have his actual lab data) .33 mmol of lactate / minute.  If we extrapolate this out to 40 minutes, he would have accumulated ~13 mmol of lactate in his legs (ouch!).  That is going to REALLY burn, and as we know, higher levels of lactate in the bloodstream lead to an increase of hydrogen ions as your body combusts the excess lactate.  This increase in hydrogen ions leads to a lower blood pH (more acidic) and decreases the work rate of your muscles as it increases (you become fatigued). (2)

In a nutshell, even though Joe’s FTP “improved”, his time to exhaustion (TTE) did not, thus, he blew up at the 40 minute mark.

To make that even more complicated, your VO2 Max (aerobic capacity) and VLa Max (anaerobic capacity) work against one another, so as 1 system improves, the other decreases, and vice versa.  This is why adopting a periodized plan, and truly “peaking” for only 1 or 2 events per year is important to properly optimize both systems to work in tangent.  The system you optimize should also be dictated by your event’s demands.

A high VO2 Max gets you to the hill, a high VLa Max gets you over first.

Common Tests to Estimate FTP

You’ll notice I keep using the word “estimate” when I refer to FTP.  This hopefully makes a little more sense after reading above, and these tests are exactly that, estimates of your 1 hour power…

Old Faithful – The 20 Minute Test

• Warm up for 10-15 minutes.
• Ride ALL OUT for 20 minutes.
• Record what your average power was for the 20 minutes.
• Multiply that number by .95.
• Voila!  You have your FTP.

This is the most common test used currently, and probably the one you’ll see during your workout plans.  Remember though, if you have a strong anaerobic capacity, or are a new rider, you can have an inflated result.  I suggest going hard and over-pacing the test for the first 3 minutes to exhaust your creatine phosphate system, and to decrease the anaerobic system energy contribution, to hopefully see your power drop and eventually plateau to your true FTP.  Ideally you’ll see a gradually increasing heart rate and subsequent power drop for the first 3-5 minutes, then a plateau for the final 15 minutes at your actual FTP.

2x 8 Minutes Test

• Warm up for 10-15 minutes.
• Ride ALL OUT for 8 minutes.
• Rest for 10 minutes.
• Ride ALL OUT for 8 minutes.
• Record what your average power was for both 8 minute tests.
• • Add both of the averages together, and divide by 2.
• Multiply that number by .90.
• Voila!  You have your FTP.

This testing protocol is the least accurate, in my experience.

The Ramp Test (Max Aerobic Power, MAP).

• Warm up for 10-15 minutes.
• Having a smart trainer makes life much easier here.
• • I start my athletes off at 60% of their FTP, and increase by 8% every minute or 2 (based on athlete fitness), until failure is reached.
• • Once you settle into a cadence of your choice you must maintain that cadence, or pedal faster, throughout the rest of the test. For instance, if you ride at 90 RPM for the test you can’t then have your cadence fall off to 85, 80 and even 75 RPM in the final stages. Once you can’t maintain your cadence the test is over, but you must push to the point of failure and not give up!

You are looking for a heart rate inflection point for this test.  The inflection point signals the lactate threshold (FTP) and can be very hard to see in my experience.  Another way is to take the last COMPLETED step of the test, and multiply this by .75.  This test is also called a Conconi Test.

The New Kid on the Block – Modeled FTP

Modeling isn’t really “new”, it has just become more available to the masses recently.  I have had great success with using modeled FTP with my athletes, and the software is becoming more accurate and robust every year.

WKO Software

WKO software is the OG is this arena.  It’s been around since I can remember with its latest iteration being WKO4.  I use this software on a daily basis, but it can be VERY daunting to the newcomer and sometimes there can be analysis paralysis with the amount of charts and data.  Fortunately, they have many educational resources, and a stand out development team

INSCYD Software

INSCYD software has recently just become available to the masses being only available to World Tour teams previously.  I like INSCYD and use it with a handful of the athletes I work with.  They claim to be the most accurate way to measure anaerobic threshold (AT), with power data and blood sampling.  Yes, yet another acronym describing kind of the same thing as FTP.  What separates them is the ability to use only power data to achieve lab quality measurements, but the testing costs are expensive.

XERT Software

I have been using XERT for a little over a year now, and have found it to be excellent.  They possess another stand out development team, and it gets better with each update.  Their modeling has also been the most accurate, in my experiences, and the value they provide is exceptional.

Closing Remarks

FTP isn’t going anywhere anytime soon.  However, like anything, there are pros and cons to using it, and the myriad of tests and software utilized to derive it can all provide different numbers.  Whatever test you decide to go with, do yourself a favor and keep the testing protocol consistent.  A result is only as good and accurate as the metrics you place into the equation.

And remember the old saying: FTP = AT = OBLA = LT = AeT = MLSS = AnT = LOL

References:

(1) Coggan, Andrew. “What Is Functional Threshold Power?” TrainingPeaks, 10 Feb. 2016, http://www.trainingpeaks.com/blog/what-is-threshold-power/.

(2) Skeletal Muscle Fatigue: Cellular Mechanisms
D. G. Allen, G. D. Lamb, H. Westerblad
Physiological Reviews Jan 2008, 88 (1) 287-332; DOI:10.1152/physrev.00015.2007