The following information was summarized from an article by Peaks coaching and written by Hunter Allen a Professional cycling coach and cyclist.

Your functional threshold power, or FTP, is the maximum power (measured in watts) you can maintain through an hour’s effort without fatiguing.

Your lactate threshold  (LT) or FTP (the level of exercise intensity at which lactate begins to accumulate in your blood) is a powerful predictor of your endurance performance ability. This is because, although your maximal oxygen uptake (VO₂max) sets the upper limit to your aerobic energy production rate, it’s your LT that determines the amount of this VO₂max that you can utilize for any length of time.

Your FTP tells you how well your muscles are able to match their energy supply to your energy demand, which in turn determines the fuel “mix” (i.e., carbohydrates versus fat) your muscles use and how they fatigue. Consequently, FTP(especially when expressed as power output) is the single most important physiological determinant of performance in events ranging from a 3km pursuit to a three-week stage race.

Your FTP provides a solid basis for any power meter-based training program, because your level of effort when exercising at a given intensity depends upon your power output relative to your power at FTP. When your power output exceeds your FTP, you’ll fatigue quickly. When your power output is just below FTP, you’ll be able to maintain it much longer.

Determining FTP

So how do you figure out your FTP? One way is to get laboratory testing done with blood samples. Determined this way, however, FTP is often significantly below what athletes and coaches think of as a threshold.

A much more convenient, simple, and possibly more accurate method of determining your FTP is to use data collected by your own power meter as you ride. There are a number of different ways to do this, all of which provide very similar estimates of FTP. I think the best way to do it is to jump on your bike and go for a ride specifically designed to find your threshold.

The Threshold Test

Your goal in this test is to average the highest watts possible for a lengthy period of time. (Hint: When you get to the main effort, make sure to pace yourself so that you don’t tire too quickly.)

The ride is laid out as follows:

1. 5-10 minute warm up
2. Opener with three 30sec intervals at lactate threshold.
3. Two steady tempo effort drills.
4. Recovery
5. 20 min FTP test (your highest sustainable effort for a 20 min time trial)
6. Three 20s hard intervals
7. Cool down.

The purpose of the drills in steps 1-3 is to open up the legs for the test, and second, to measure your ability to produce watts in the VO₂max power zone. This effort also helps to dispense the “freshness” that always exists at the beginning of a ride; your next effort will produce power that is more likely to be truly representative of your FTP.

Your goal in the main portion of the test (the 20-minute segment) is to produce the highest average watts possible over the entire time. The test doesn’t work if you start out too hard and suddenly run out of energy, because you won’t be able to produce your true maximal, steady-state power. It’s always better to start out in the first two minutes a little under what you believe to be your FTP, build up along the way, and then ride at your maximum level in the last three minutes.

Now that you’ve done the test and downloaded your data, find your average power from the entire 20-minute effort. Take this number and subtract 5% percent from it. The result is your functional threshold wattage value. For example, if you averaged 300 watts during the 20-minute time trial, 5% of 300 (300 x 0.05) is 15, and 300 minus 15 is 285. Your FTP is 285 watts.

The reason for subtracting 5% from your average watts during the 20-minute test is that your true FTP is the highest average power you can maintain for sixty minutes. Most athletes have a hard time putting out maximal effort for sixty minutes, however, and those who can learn very quickly that a sixty-minute time trial is not much fun. I’ve found that twenty minutes is a more realistic time frame. It’s obviously a shorter time period, however, and it incorporates more of the athlete’s anaerobic capacity, which skews the wattage data by about 5% over a sixty-minute effort. By subtracting that 5%, you end up with a wattage number that should be very close to your true FTP.

Avoid strenuous exercise 48 before the test so your legs and lungs are fresh and well rested for an accurate test.

Ready? Go! What’s your FTP?