Functional Threshold Power (FTP) Quick Guide

What is FTP?

Perhaps the most popular definition of Functional Threshold Power (FTP) is “the highest power a rider can maintain in a quasi-steady state without fatiguing. It is an estimate of the power output that corresponds most closely with the maximal metabolic steady state or metabolic control limit, or what is more commonly referred to as threshold.” (See Training and Racing with a Power Meter, by Andrew Coggan.)

However, in the last several years, many other authors and publications in the media shared their own views and definitions of FTP. And because FTP has many limitations, physiology experts, coaches, and athletes are increasingly opting for other methods of determining their threshold and training zones.

Lastly, note that FTP is different than Lactate Threshold, another useful measure for determining exercise intensity for training and racing in endurance sports.

Is FTP important?

FTP is a training tool. It is one of the many tools athletes and coaches use to train with purpose, increase fitness, and get faster on the bike. Regardless, you will need a similar measurement to be able top determine your training zones.

Cycling coaches typically design workouts by using power zones as a percentage of your FTP, or by prescribing intervals to be done at specific target watts for a certain duration.

Nevertheless, FTP is perhaps the most popular training tool because any athlete can easily estimate it on their own, as discussed further below.

How do I measure my FTP?

There are several ways to measure FTP through riding, indoors or outdoors. These are typically referred to as “FTP tests”.

The 20-minute test

The most popular and commonly used test is the 20-minute time trial. In this test, the goal ois to produce the highest average power possible over 20 minutes. The FTP is calculated as 95% of the average power produced over the 20-minute period.

For example, if your average power for the 20 minute effort was 100 watts, your FTP is 95 watts (100w x 95%).  Why 95%? Because “in theory”, if you can ride at 100w for 20 minutes, you should be able to ride for 95w for 60 minutes.

That’s the theory. However, many scientists agree that this methodology tends to result in an FTP number that is higher than the actual number an athlete would actually be able to sustain for 60 minutes.

Therefore, athletes should be careful with potential overtraining, fatigue and injuries that might result from using an FTP from the popular 20-minute test.

The 60-minute test

Further, Dr. Stephen Seiler, one of the most respected authorities in exercise physiology, says that a 60-minute time trial is a more recommended and realistic way to determine an athlete’s threshold.

Moreover, there are other ways to measure your FTP, and the science of performance is quickly evolving. Take a listen to this Fast Talk podcast on the reasons why FTP might not be the “end all, be all” measurement for training.

How often should I test?

The frequency of testing should be coordinated with your coach. In the early stages of development, testing every three months is quite satisfying because improvements can be quite significant.

Over time, and if you are a more seasoned athlete, FTP growth will slow down, making the test frustrating at times. I personally like to use other tools, such as WKO4 software, to adjust athletes’ FTP as needed over time, without the need to put them through a 20 or 60-minute test.

Also, keep in mind that FTP is not a static, absolute number. It can vary depending on circumstances outside of the athlete’s control, such as altitude, air temperature, illness, fatigue and others.

FTP Tests on Zwift

A convenient option is to perform an FTP test on Zwift by selecting any of the two available workouts, described below. Both use the 20-minute test approach discussed above. Upon saving your ride, you will be notified of your FTP.

FTP Test – Standard

The standard test on Zwift starts with a 20-minute ramp that goes from 30% to 70% of FTP. Next is 3 sets of 3 intervals, each for 20 seconds at 90%, 110%, and 130% of FTP (9 minutes total), followed by 5 minutes at 60%, 5 minutes at 110% and 10 minutes at 60% of FTP.

Then the test starts with a 20-minute block where you ride as hard as you can sustain for that duration. Cool down for 10 minutes.

FTP Test – Short

This version of the test has a shorter warm up. It starts with a 5-minute ramp going from 30% to 70% of FTP. The next set is 3 intervals of 20 seconds each at 90%, 110%, and 130% of FTP, followed by 3 minutes at 60%, 3 minutes at 110%, 2 minutes at 120%, and 6 minutes at 55% of FTP. 

Then the test starts with a 20 minute block where you ride as hard as you can sustain for that duration. Cool down for 5 minutes.