Submax FTP Calculator

Alan Couzens, MS (Sports Science)

As you might have guessed from yesterday's post, I'm, generally, not a big fan of doing a lot of sustained work in or around the athlete's FTP. In relative terms, this is true throughout the year, but it's especially true in the early season, when both overall volume and the fitness base of the athlete is at the lowest point of the build. For most athletes, a 20min max TEST effort at or above FTP in the early season constitutes 'way too much' FTP work in my opinion/experience.

For coaches who use performance modeling software (WKO+, Training Peaks etc.) this represents a problem, as many of the calculated metrics rely on having an accurate, up to date, FTP number entered for the athlete &, at least to this point, the way to produce that number was via a maximal effort of at least 20min duration.

When a major unload is included (as it should be each year), there is a significant drop in the athlete's FTP number. For a good level AG male, this is typically in the range of 30-60 watts! If FTP is not adjusted, the training load (TSS) of each session will be significantly underestimated. This can lead to big problems in terms of over-doing the training load prescription and can even lead to an early season bout of overtraining that can really mess with the upcoming season. Bottom line: You shouldn't use last season's FTP number at the start of a new season.

But... we do need a number and the alternative to using last season's isn't a whole lot better in terms of risk of over-training. Do we really want our athlete to be blasting a "bleed from the eyeballs" 20min max effort coming straight out of a "keep moving but don't do anything structured" off-season prescription? I can attest from experience that we don't! Bad things happen when athletes with no aerobic base start doing maximal anaerobic efforts!

So, what's the solution?

I'll offer one here - a submaximal FTP calculator that uses the relatively linear relationship between HR and power (or pace) within the athlete's aerobic zones to 'project up the line' to what the athlete's FTP would be at threshold heart rate.

What you'll need....

* A true max heart rate value - this could be from any recent season as max HR is a relatively stable number.

* A current resting HR number.

* 2 submax efforts on a flat road/trainer where you lap for power or pace and HR. Ideally you'll come back to the same course for each test. Also, ideally you'll do the test under similar conditions (similar time of day, temp etc). These efforts should be sufficiently long that HR stabilizes for a good period of time but sufficiently short that decoupling isn't significant. Depending on fitness, something in the range of 2x10min to 2x20min works well.

* Do the first as close as possible to (but not exceeding) the top of your Steady heart rate zone (indicated by the HR number next to 65%)

* Rest for a sufficient period of time to bring HR & power back in line.

* Do the second as close as possible to (but not exceeding) the top of your Mod-Hard HR zone (indicated by the HR number next to 75%)

If you know your specific % MaxHR numbers (from a lactate test) for top of steady, mod-hard & threshold heart rates,, you can change the % numbers and enter them in the calculator. If not, use the recommended 65, 75, 85% Karvonen numbers given.

* Enter your average power or pace from the 2 intervals of the test in the white squares.



The calculator will spit out an estimate for your current functional threshold power or pace that you can then plug into Training Peaks or WKO+ to ensure more accurate TSS numbers in the early season.

When fitness improves and training shifts to include some more threshold work in the program, you can shift to the CP5/20 FTP/fatigue curve calculator for a more accurate estimate of FTP and more extensive assessment of strengths and weaknesses. This is a more informative test, but the athlete has to have a certain amount of base fitness to be able to include these tests on a sufficiently regular basis without it negatively affecting their training.

Hope you find it as useful as I have with my own athletes.

Train smart,

AC