Some cycling experiences around the CP curve

Hi there ! With the end of the COVID19 lockdown I was eager to challenge myself. I did several critical power tests to assess my fitness and have the feelings of all out challenge like a race would be.

I had a good block of training with a lot of endurance on the bike and solid 4×8 min efforts around 90% of my HRpeak. Mid April I felt really good. This fell apart a little bit with a streak of on calls at the hospital. I put emphasis on sleep and recovery before engaging in a series of tests.

I did several max efforts in the same conditions : on my trusted TacX Neo, on the TT bike, in the morning, feeded, room temperature around 21 Celsius degrees, 45% humidity, fans on, beverages available (a pinch of sodium bicarbonate with 2 spoons of maltodextrins per bottle)

Here are the duration of the efforts : 4, 6, 20 and 60 minutes. It was the first time I did a 60 min effort. I had this idea after listening to a podcast with Stephen Seiler with the idea of getting my personal ratio between a classic 20 min test and a 60 min test. The shorter tests to evaluate my max aerobic power. I have found a study by Grappe where the 4 min effort correlate well with max aerobic power, and also 6 min effort is often considered like a good effort to reach a VO2MAX plateau and Pr Seiler takes this reference for his endurance durability rides (another thing to test in the next weeks, I guess my IN/EX S ratio will be superior to 1, but the interesting part is to watch for decoupling when the effort lasts a long time)

In the last two years, I mostly did short (10 minutes) all out efforts. I think my coach was willing to get rid of my pupil mentality since I took every all out effort like an important test. Notice that he never gave me power or heart rate goals, only RPE goals and I had tremendous results this way and I am super thankful to him. But this year I wanted to ease off the competitive edge and work on my discipline to build myself a balanced program.

Let’s speak numbers. I weight 62 kg. I am 39 y/o. I am cycling since the end of 2014 with the goal of doing long triathlons and century rides. I sincerely don’t know what FTP is but it has been around 3,75 W/kg and 4,25 W/kg in the last years. My resting HR is 41 according to Garmin and My HR peak is 180 on the bike.

Frankly, the 60 minutes effort was the effort that looked like an endurance feat to me. On the 20 minutes effort, there is this goal of going all out to reach the highest number possible and I think it skews the endurance test a little bit.

Here are the numbers :

  • CP4 351 W
  • CP6 329 W
  • CP20 285 W
  • CP60 257 W
CP 60 is draining

I am happy with it, all are PR, but I didn’t had great feelings during the tests. I could have been more fresh. I didn’t have a bliss experience like we sometimes have when the RPE is lower than we expect during a strong effort.

CP curve from

I don’t want to turn this blog note on a review on FTP versus physiological measurements in the lab with cart metabolic testing, but I agree that setting one’s « FTP » at 95% of an all out 20 min efforts is at great risk at putting you under great stress if you calibrate your workouts with percentage of FTP goals. My ratio between CP20 and CP60 is 90%

For example, during the 4×8 min Seiler workout, the goal was to achieve the highest effort sustainable for the 4×8 minutes. Of course there is some kind of a learning curve here but at some point you feel the right dose of effort. The resulting physiological datas in his cohort was a power around 106% of their 4 mmol/l of lactate power and 90% of their HRpeak. When I started this block of workouts, Garmin/Firstbeat gave me a FTP around 245. Doing 260 W (245×1,06) was really hard for me and my HR drifted toward the max. Firstbeat gently adjusted my FTP around 230. Then I gained some fitness, and was able to maintain 270 W during the 8 min efforts, my HR was spot on, so I estimate my « FTP » around 250ish. The XERT Connect IQ datafield also gave me this calculation. Notice that Fast Fitness Tips also shares a cool spreadsheet to have an idea of you power-duration curve with more realistic numbers than 95% of CP20 gives FTP. They also have a good video on this topic on You Tube. I have sensible ears so I warn you, turn the volume down since the author likes to emphasize his ideas with loud booms.

Using FTP to get a power goal during a race is key for some triathlete. (I think it’s super important to work on feel and maybe to keep an eye on HR at some point) In the past I have used the 95% rule to determine FTP and noticed that I could aim for 78% of FTP during an half IM. With a more conservative approach to FTP I could go for a traditional 80% of FTP and it would be in the same ballpark (200ish W during the bike leg of a 70.3 triathlon)

Just a few last anecdotes about getting a FTP number. In the last months, I have been pretty happy with the training load and fitness evaluations from my Garmin Fenix 6. During my tests, my Firstbeat VO2MAX went down and the watch kept saying I was “unproductive” despite PRs. I find this a bit surprising but I would say it’s somewhat logical since I felt in worse shape than 15 days ago. And despite having done a 60 min effort with a higher power than my Firstbeat FTP, my Garmin/FB FTP didn’t increase. I think their algorithm studies the HR in a savvy way and my breathing during the CP60 was quite heavy and I might have been above the second ventilator threshold at some point with a respiratory rate above 40. It would have been fun to share some footage with you but I think You Tube thinks it’s Porn since my video was quickly censured. emoji-LOL

Last stuff : the XERT data field calculating FTP seems to take a 40 min max effort as FTP since during my CP60 Xert-FTP was equal to my avg power at the 40 min mark. But I give some credit to this data field. If you do a super solid effort on a short timeframe it will give you quite a good estimate of you FTP. Maybe a little bit too optimistic for me… (Note that Baron Biosys recommends using their data field under fatigue to get realistic figures)

After 40 min of effort

Eventually I encourage you to test and send some money to the developer if you find it cool. I have discover this web app taking advantage of your Strava data recently and I find it neat.

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