Functional threshold power (FTP) is a key metric for cycling performance. Defined as the maximum average power a cyclist can maintain over a one-hour effort, functional threshold power is particularly important for time trial specialists and for short-course and Olympic distance triathletes who need to know how to pace their effort over thirty-to-sixty minutes.
FTP is also important for road cyclists. While FTP will not help a roadie win a sprint, a road cyclist with knowledge of his or her sustainable watts may be able to plan an attack, go off the front of the pack and hang on for victory in the closing kilometers of a road race. Likewise, roadies with knowledge that their FTP may be limited with respect to the stronger riders in the group may be wise to sit in and conserve energy in the pack, then go for victory in a sprint (requiring strong sprinting skills, of course).
How to Determine Functional Threshold Power
Determining functional threshold power, also referred to as lactate threshold power, requires a bike configured with a power meter. The ideal way to determine FTP is to warm up, find some clean road or a long hill to climb, and ride as hard as you can for one hour. Start out at an easier pace than you think you can sustain, and build the effort over time. The resulting average power over the one-hour effort is your functional threshold power.
If you are not into suffering for an hour, a 20-minute threshold effort, also referred to as a 20-minute critical power (CP-20) test, may suffice as a proxy for FTP. The 20-minute test is similar to the sixty-minute test – an all out, sustainable 20-minute effort. But since a cyclist can sustain a harder CP-20 effort than a CP-60 effort, a factor of 92-95% of the average power from the 20-minute power test is used to estimate FTP.
20-Minute Power Test Protocol
- Spin easy for 20 minutes building to endurance pace
- Do 4 x 1 minute hard efforts to open up and start the lactate buffering agents, on 3 minute recovery
- Start the test at a strong, sustainable pace
- Build gradually over the first five minutes, then hang on for the duration of the interval
- With 3 minutes to go, drill it, leaving nothing on the table
Below is graphic image of a 20-minute power profile test. Upon recommendation from his cycling coach, this athlete started out at 260 watts for the first five minutes, then built to 270 watts for the next five minutes, before bumping to 280 watts at the 10-minute mark. Over the final two minutes, he gave it all he had at an average of 286 watts. For the entire effort, this cyclist averaged 271 watts. Using a factor of 95% of that figure, this athlete was determined to have an estimated function threshold power ability of 258 watts.
According to Hunter Allen, co-author of Training and Racing with a Power Meter, a cyclist should begin by establishing a solid foundation of training to include both tempo rides at 80-88% of FTP and “sweet spot” rides with intervals at 88-93% of your FTP over 6-8 weeks. He also recommends doing at least one long ride on the weekend of 4-6 hours in duration as a means of stressing the aerobic system and building fitness. Then, an athlete seeking to improve cycling performance can begin to do more interval work at 100% to 105% of FTP as a means of further improving sustainable power output.
By working on improving your FTP, an experienced cyclist could expect to make gains in FTP ranging from 3% to 10% on a year over year basis. With those gains in FTP comes an improvement in cycling performance. It’s hard work, and gains do not come easily, especially for aging cyclists fighting inevitable declines in V02max. But by staying focused on improving your FTP, you can become a stronger and faster cyclist.