FTP, or Functional Threshold Power, is a method to determine the onset of lactic acid. Like the Conconi test in the 80’s, it is a simple, yet inaccurate way to estimate the onset of lactic acid. Because it uses (relatively) cheaper methods than a CardioPulmonary exercise test, it has become popular for the training programs that are unable to interpret testing protocols.
Under the current model for Functional Threshold Testing, a cyclist rides for 20 minutes, essentially going all-out for those 20 minutes. The average power during the 20 minutes is supposed to represent the wattage at the onset of lactic acid for those without access to CardioPulmonary Testing (1).
Considering that there is no system in the human body that is maxed out at 20 minutes, this isn’t a valid test. Studies that have tried to replicate the validity of the FTP have fallen short. Specifically, one study found that “coaches should be cautious when using FTP and power outputs at laboratory-based thresholds interchangeably to inform training prescription.”(2) In other words, FTP can not be used to replace real measured values such as the onset of lactic acid or threshold.
Keep in mind that a 20-minute time trial does not represent the maximal use of the Type I muscle fibers which it is supposed to represent. The Type I fibers are maximally used after a 60-75-minute time trial. During a 20-minute test, all the Type I muscle fibers are used and some of the Type II fibers are used, which does not give a valid estimation of threshold power. Think about it this way: if you have the same pace for a 5k and a marathon, you aren’t pushing yourself hard enough for the marathon.
FTP only gives us one number and the rest of the zones are still estimated based off this number. This is like determining heart rate training zones by estimating maximum heart rate, something that endurance athletes haven’t used reliably for years, and with good reason. To truly measure (not guess) training zones, a cardiopulmonary exercise test which measures oxygen use (VO2) and carbon dioxide output (VCO2) is still the gold standard.
(1) Denham J1, Scott-Hamilton J, Hagstrom AD, Gray AJ. Cycling Power Outputs Predict Functional Threshold Power And Maximum Oxygen Uptake. J Strength Cond Res. 2017 Sep 11.
(2) Sanders D, Taylor RJ, Myers T, Akubat I. A field-based cycling test to assess predictors of endurance performance and establishing training zones. J Strength Cond Res. 2017 Mar 25.
Michael Ross, MD is a sports medicine physician who has been treating endurance athletes for over a decade. He has been a team physician for numerous professional cycling teams. He also runs the Rothman Institute Performance Lab, a medical and scientific exercise testing and training facility in Bryn Mawr, Pennsylvania. He has written two books on training and sports medicine for endurance athletes as well as multiple scientific papers. He has been an invited speaker at USA cycling and consulted for several bicycle companies to provide the optimum fit. He is an avid triathlete himself who has qualified for short course triathlon nationals several times. When he is not at work or spending time with his family he can be found on the trails and the roads around Philadelphia. www.rothmaninstitute.com/physicians/michael-j-ross-md