Is Cycling FTP an Accurate Measure of Lactate Threshold?
Updated: Oct 25, 2018
Is a 20-minute time trial on the bike a valid way to prescribe training intensities on the bike and is it the same as anaerobic threshold?
Functional threshold power is defined as the highest power output a cyclist can perform at steady state for one hour (FTP60). For cyclists, a logical way to test and evaluate their FTP60 is to pedal for 20 min all out and use 95% of this number (FTP20). This FTP20 output is often used to prescribe target intensity zones for training. The question is, how valid is this method? Is this a real representation of what someone can hold for an hour? How close are these numbers to your true FTP? So now with this number the athlete can supposedly work on different areas of fitness such as lactate threshold, etc. But, how does FTP relate to lactate threshold?
When an athlete discovers their lactate threshold, this number gives them three exercise intensities. Two of the intensities are anaerobic threshold and aerobic threshold. Most athletes don’t have access to a lab and blood samples to test this. This is why many athletes develop zones based off heart rate or power output. FTP should resemble anaerobic threshold when testing blood lactate (also called maximal lactate steady state). Too many terms!! So the idea is…for an hour at this power output or lactate measurement you won’t fatigue but if you go over an hour…you will start to, and it won’t be pretty.
How accurate is FTP compared with a person’s individual anaerobic threshold? This testing method had yet to be thoroughly investigated with FTP20 despite is prevalent use in the endurance community. Previous studies have shown that FTP8 (8 min TT then multiplied by 90%) was incredibly accurate at estimating anaerobic threshold. A couple researchers based out of the University of Kent and the University of the State of Santa Catarina decided to take a deeper look and designed a study to test this theory.
23 trained male cyclists were involved in this study and put through some grueling tests. These tests consisted of a graded exercise test (which started at 100 watts and increased by 40 watts every 4 minutes until the cyclists said mercy), a 20 min time trial, a 60 min time trial, and a time to exhaustion at their calculated FTP20. If you haven’t done any of these tests, then you don’t understand the pain associated with trying to go all out. For this reason, they separated each test by 48 hours.
Blood was taken for lactate analysis, oxygen consumption was measured, heart rate was constantly monitored, and the Borg scale (6-20) was used so participants could tell the researchers how hard they were working.
So what do you think? Is FTP20 a good representation of FTP60?
The study found large to very large correlations between FTP60, FTP20, and IAT for power output. The similarities were so close. Power outputs for the variables were FTP60 (231±33W), FTP20 (236±38W) , and IAT (237±29W). Time to exhaustion at these power outputs fell within the expected ranges.
One researcher from another study, Sanders et al., found that from those studies FTP8 overestimated several LT methods. The differences were sometimes 6% which led to sometimes 20 watts higher than the actual value. These differences were probably because the researchers used different definitions and methods for concluding how to measure lactate threshold.
With this being said, this study suggests that with this information, 20 min and 60min TT’s should be the gold standard for analyzing FTP (instead of using an 8 min TT)
Some interesting data. At the end of the study, the researchers write that the 20 min TT should be used for training prescriptions WITHOUT the 5% subtraction. They believe that the PO of the 20 min is “comprehensible” enough to provide a coach or an athlete with strategies and insight on how to write a workout. This was a complicated study to read. The conclusion that I have come is this study has shown that these testing methods are valid. Even though they found strong correlations with the tests within the large group as a whole, individuals sometimes showed different correlations between variables. These tests should not try to be used interchangeably, meaning if you’re doing a race that will take an hour, the best predictor of your mean power output will be an actual hour time trial. The FTP20 should be used strictly for training and for estimations of longer racing.
When I raced Atlantic City in September, early in the year my 95% average of my 20min TT was 294. As the season progressed and as I tested this number outside I found my new number to be 304 (this was with a really technical course so probably still not accurate.) The estimation for Ironman 70.3 can be 80-85% of your FTP. 80% is 243 and 85% is 259 and I held 260 for the 2 hours and 16 min. Some might say this is too high, but I had a great performance and with an average HR of 143 I felt like I could have pushed harder.
Take this information, digest it, and use it to be analytical in your own way. Don’t form definitions and tell yourself that any study gives you 100% correct information. The research is just demonstrating with a certain level of confidence. The better test is for you to go out and see who you are an an individual during different distances and different intensities. The test is the exercise and the exercise is the test.
My professor Dr. Lunn has us practicing writing abstracts with the research we are investigating. The students try to look at the already created abstract and create our own. Here's my attempt. I love how Word underlines the methods for testing.