“If you can’t deliver a certain level of power or performance in training then the chances are you’re not going to be able to do it in competition.” (Chris Boardman)
Before using the CyclingPowerLab supplied power zone calculator, you’ll first need to determine your FTP (Functional Threshold Power). There are multiple methods to determine FTP, both direct and derived. For the direct method, ideally, the rider would complete a maximal 60 minute time-trial effort. The average power for this period would represent their FTP. However, it’s useful to repeat FTP testing at regular intervals and a 60 minute TT generally proves be too fatiguing and mentally stressful for most athletes to undertake regularly enough.
“FTP is the highest power that a rider can maintain in a quasi steady-state for approximately one hour without fatiguing.” (Hunter Allen & Andrew Coggan)
Dr. Andrew Coggan suggests that 95% of average power over a 20 minute effort provides a good estimate of an athlete’s FTP. For example, if I average 310 watts over a 20 minute effort, using Coggan’s formula, I’d estimate my FTP at 295 watts. This may result in an overestimation for some riders, but it’s a good place to start. A 20 minute test is certainly easier on the mind and body than a 60 minute effort.
If you’ve never done an FTP test before, you’ll have to make an educated guess about what power you can maintain for 20 minutes. If you’re using TrainingPeaks to log your training and racing, you can use the ‘Peak Power’ graph in the ‘Dashboard’ view to identify your best 20 minute effort since you started recording sessions. This average power is generally a good place to begin for riders conducting their first 20 minute effort test.
To control the environment, making it easier to repeat the protocol and compare results, the test can be conducted using a turbo trainer. If the rider can find a clear and safe stretch of road, it’s also possible to conduct the test in the field. (You can read about the difference between testing in the laboratory vs. the field, here). With regard to pacing the 20 minute effort, the rider will generally return their best average power by beginning the test at an intensity that feels slightly too easy, build gradually and, ideally, push hard in the last minute to finish the test completely exhausted. However, even if the rider starts too hard and ‘explodes’, or ends up feeling that they have more left to give, it’s still possible to learn something useful. Each time you do the 20 minute test, you will get better at pacing your effort in order to return the best, most representative result.
Once you have the data from your test, plug the numbers into the calculator and see what you come up with!