This will be old hat to anyone that's been around the world of training with power meters for some time. However, having monitored the cycle training forums lately, it seems the question about how to estimate a rider's Functional Threshold Power (FTP) is something that comes up quite regularly.
So I thought I'd write a post about it in the hope that it will at least help clarify one or two things for people.
Before I go into the various methods used, it's probably worthwhile quickly revisiting what FTP is and why it is important to know.
FTP is a practical and readily measurable indicator of a rider's aerobic fitness. It was introduced to the world by Dr Andrew Coggan and for all intents and purposes it removes the confusion that exists over the term "threshold" and all of the various terms associated with it.
It is important to know FTP for a number of reasons:
-- threshold power is the single most important physiological determinant of endurance cycling performance (covering events from individual pursuits of 2 km long, up to stage racing lasting several weeks). Hence improving FTP needs to be the primary focus of our training, and measuring FTP on a regular basis is an excellent means of tracking fitness changes through the course of a season.
-- it enables a rider to define and measure intensities of riding (or power levels) relative to their own current level of fitness, expressed in a manner that relates to the primary physiological adaptation that occurs at each intensity (power) level. This is very useful for guiding training and making sure that the mix of intensity and duration during a workout or training cycle is appropriate for gaining the specific fitness required for a rider's target events.
-- it is a key input into other metrics which enable a rider/coach to monitor overall training stresses, both long term training loads and recent fatigue levels.
-- it also provides an excellent guide to how a rider should most effectively pace themselves, especially in races such as time trials (or during a breakaway in a road race or criterium)
Of course you need to have an on-bike power meter or a stationary ergometer that measures power in order to measure or estimate FTP.
FTP is simply defined as follows:
"FTP is the highest power that a rider can maintain in a quasi-steady state without fatiguing for approximately 1 hour.
When power exceeds FTP, fatigue will occur much sooner, whereas power just below FTP can be maintained considerably longer".
Okay, so that's easy. If you want to know your FTP, just go out and ride your bike as hard as you can for an hour and see what the average power was. In essence this is the gold standard measure of a rider's FTP. Unfortunately it is not always possible nor practical for everyone to do a one hour time trial like test. And not all such tests are well paced. A poorly paced effort may result in a lower average power than a well paced effort.
So what are all the alternatives available to us to estimate FTP?
Well, Dr Coggan kindly made a list of these, titled "the seven deadly sins" and posted them to the wattage forum in June 2004. Here is the original post reproduced:
"the seven deadly sins....
...er, ways of determining your functional threshold power (roughly in order of increasing certainty):
1) from inspection of a ride file.
2) from power distribution profile from multiple rides.
3) from blood lactate measurements (better or worse, depending on how it is done).
4) based on normalized power from a hard ~1 h race.
5) using critical power testing and analysis.
6) from the power that you can routinely generate during long intervals done in training.
7) from the average power during a ~1 h TT (the best predictor of performance is performance itself).
Note the key words "hard", "routinely", and "average" in methods 4, 6 and 7..."
Okay, so #7 is obviously the "Gold Standard". What about the others?
Inspection of Ride File / Power Distribution Profile
#1 and #2 require you to inspect data using power meter data analysis software. The method is described in more detail in the book "Training and Racing with a Power Meter" by Allen and Coggan. In general these two methods are more useful as a means to check whether a rider's FTP may have changed, than for estimating FTP itself. With #2, it is important that the selection of ride files chosen contain efforts such as races or very hard training.
Blood Lactate Measurements
#3, done properly, usually requires you to visit a sports science laboratory or a well set up cycling coach's facility. Even then, interpretation of the blood lactate data may not result in practical information for the rider. If you have a power meter, there really is no need to have a blood lactate test performed.
Normalised Power (from a Hard ~1hr Race)
#4 is pretty handy, particularly as an indicator of when a rider's FTP may have changed. Frequently riders who do not do time trials, but do other races such as shorter road races or criteriums of approximately 1 hour duration, can use this as a crosscheck of their current FTP. Assuming the race was hard (that is, you were pretty much on the limit for most of the race), and you were not overly fatigued beforehand, then the 60 minute maximal Normalised Power should be at least at your FTP if not a little higher (up to about 5% higher). If your 60 minute Normalised Power is reported as more than 5% above your FTP, then that is a strong sign that your FTP needs re-setting (upwards).
#5 is also a very useful means of estimating FTP. It explores the relationship between work performed (kJ) and duration (seconds). Essentially all you need is at least two (or more) maximal efforts of at least three minutes and less than 30 minutes duration, say one of five minutes and another of 20 minutes, although the choice is arbitrary and up to the individual. You then enter the average power and durations ridden into the Critical Power model. The model will calculate what is called "Critical Power", which is essentially equivalent to FTP (or at least a very good estimation of FTP).
A couple of notes: the "test" rides chosen should have been performed within a reasonably close timeframe (say within the same week), and should not be cherry picked from other rides. They need to be stand-alone maximal efforts. It is also preferable to have two very good data points rather than three or more unreliable data points. I recommend reading about it here (this links to a pdf document by Eddie Monnier) and downloading the spreadsheet as well. It also helps to use the same (or very similar) durations for all future Critical Power test inputs.
#6 is great for riders that regularly do hard aerobic interval work, especially indoors. The intervals need to be of sufficient duration, I would say at least two efforts of 20 minutes (with a short break between) at time trial power/pace. When done on an indoor trainer, then it is common for longer maximal effort intervals of 30 to 40 minutes be nearly equivalent to FTP. As training progresses over the weeks and months, then changes in sustainable power during these intervals is a great guide to changes in FTP.
I'd suggest the Seven Deadly Sins also include the following methods:
5a) by conducting a Maximal Aerobic Power (MAP) test, using the test protocol on Ric Stern's website . FTP typically falls within the range of 72%-77% of MAP.
An example of a MAP test can be viewed here.
Shorter Time Trials
5b) by conducting a time trial effort of sufficient duration (say at least 20-min), with FTP typically falling into a range of percentages for TTs of this duration e.g.:
- FTP = 93% +/- 3% of 20-minute maximal average power
- FTP = 94% +/- 3% of 16km (10-mile) TT avg power
Of course everyone is different and some may fall outside of these ranges.
There really is no reason to nail it down to the nearest watt. Setting FTP to the nearest 5 watts is sufficient. I only change the FTP setting if there is hard evidence of a change of at least 5-10W.
Of course, getting the number right does depend on ensuring that a rider's power meter is correctly calibrated and any zero offsets needed are done. Strange numbers are usually strange for a good reason.
Remember, these are all just ways of estimating FTP and some are better than others at nailing down the number (and for many, some are more practical to perform than others). The final two methods for example, would typically get you to within a few percent either side and can then be cross referenced with another method.
It all depends on a rider's circumstances. Not everyone is in the position to do a ~1 hour time trial with sufficient regularity.
What do I use?
For the purposes of tracking aerobic fitness changes, and the setting of training levels, then performing a Maximal Aerobic Power test, combined with one of the other tests for FTP (usually a 16km or 40km time trial), is the method that I typically use with my coaching clients. Having this combination is particularly useful when assessing the training priorities for an athlete.
Of course, you can always track fitness and base training levels on a mean maximal power for a duration of less than 1 hour (e.g. a 20-minute test, or as has been suggested, 2 x 8-minute test efforts). However, by doing so you start to introduce the influence of anaerobic energy production into the test result, which means you may not be entirely sure which component of your fitness is changing, and hence be uncertain as to what type of training is needed in order to progress further.
So which sin will you choose?
This isn't the end of it of course. There are still a multitude of factors to consider, such as the impact of the following on FTP:
- Environmental effects
- Point of training cycle
- Chronic Training Loads
- Training Stress Balance
- Hills vs Flat terrain
- Different trainer types
- Different bikes and rider positions
I'll save that for another post.....
1. Coggan, A. Ph.D, Allen, H. Training & Racing with a Power Meter, Velopress 2006.
2. Monnier, E. Using the Critical Power Model to Predict Various Points Along the Power-duration Curve. http://velo-fit.com/articles.htm, 2004
3. Stern, R. What is MAP?, http://www.cyclecoach.com/pageID-news-Test_yourself.htm, 1999