Few components of power-based training are as important as measuring and tracking FTP. In fact, it could be argued that nothing short of actual performance ranks as highly in terms of overall importance. With this in mind, we offer the following primer on what your FTP represents, what an FTP test is, how and why we assess FTP, and when we assess it.
What is FTP?
Functional Threshold Power is — quite simply — a measure of fitness.
FTP represents the power (measured in watts) that you could theoretically maintain for about an hour, and it's the single metric we use to scale each of your workouts in our shared quest to keep your fitness growing.
With regards to what's taking place within your body and the muscles themselves, riding at your FTP pushes you right up to that limit where pushing any harder will drastically limit the duration of your ride.
But as long as you stay just below that acidic tipping point where your muscles light up and uncomfortably tolerable minutes become barely tolerable seconds, your muscles are in balance with the workload - for about an hour, anyway.
What is the FTP Assessment?
An FTP assessment is a snapshot of your fitness at any point in time. By measuring your fitness and assigning it a number, we can track changes in your fitness over weeks, months, even years.
How is FTP Calculated from the Tests?
TrainerRoad will automatically calculate your FTP upon completion of your test workout. Here is how we calculated FTP's for each testing format:
20-Minute Test: Your average power for the 20-minute interval is multiplied by .95 to get your FTP. In other words, your FTP is 95% of your 20-minute power.
8-Minute Test: Your average power for the two 8-minute intervals is multiplied by .90 to get your FTP. In other words, your FTP is 90% of your 2x8-minute power.
How is Functional Threshold Power Assessed?
During an assessment, riders first follow a consistent, structured warm-up before riding at a challenging effort level for an extended period of time, e.g. 20 minutes or 8 minutes.
The power that you average over these sub-hour durations allow us to mathematically estimate what sort of power you might be able to sustain for up to a full hour.
The goal here is to obtain a reasonably close estimate of one's sustainable power, or in power-based training nomenclature, your Functional Threshold Power/FTP.
Why Do We Assess FTP?
By assessing FTP, not only can we track changes in fitness but we can also establish training zones, i.e. power levels. And as your fitness changes, we can update these power levels accordingly.
Each type of interval, e.g. Tempo, Sweet Spot, VO2max, etc. represents a percentage of your FTP. For example, Tempo intervals fall in the 76-90% FTP range while VO2max intervals fall in the 106-120% FTP range.
Different types of intervals target different energy systems and consequently different training adaptations, so it's important to have a personal measure of your fitness that will allow us to tailor your workouts to your specific needs and capabilities.
When Should I Assess My FTP?
It's a good idea to assess your FTP prior to beginning each training season unless you already have a good sense of your current fitness and your sustainable power. But even if you think you have a good grasp on your current fitness, it's still a good idea to back up your perception with actual performance.
It's also recommended that you assess or reassess FTP before embarking on a new training plan.
Finally, you should reassess your FTP about every 6 weeks in order to account for changes in your fitness and to keep your power levels in line with your performance potential.
What if I'm Feeling Stronger Before My Scheduled FTP Test?
Of course, testing roughly every 6 weeks is just a general guideline. Your FTP very well may have increased prior to 6 weeks after your last test. If you find yourself breathing easy through workouts with high IFs or that you're often manually increasing the workout IFs before it's time for your next test, don't hesitate to raise your FTP. No need to wait for an FTP test if you know you're stronger. :)