This is a good read IMO.
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nice!!!
I like reading Jemâs stuff but that was a little deep.
Coggan is brief but accurate if you understand the last 100 years of exercise physiology around this upper aerobic threshold. Thats why few âget itâ when reading Cogganâs stuff.
Here is my view⌠its based on my own observations from first year of training, and most recently reading Scientific Training for Endurance Athletes by Dr Phil Skiba. Great book by the way.
FTP is a field tested small range of power, maybe 5-10W, that is the border between stable and unstable physiology.
All I can observe on the bike is my heart rate and breathing and power. You can learn a lot by paying attention to those 3 things.
Unstable physiology / severe intensity domain
If I properly pace a really hard 3-6 minute effort, my breathing keeps increasing until its feels like Iâm drowning for air, my heart rate keeps climbing towards max, and I literally stop by blowing up. Thats unstable.
If you go above FTP and have good estimates of ftp/cp and anaerobic capacity, you can estimate the time to blowing up almost down to the second.
Unstable physiology / extreme domain
All-out short sprints, say a 30-second max effort, you fatigue and blow up before reaching max breathing (VO2max). Thats also unstable but without reaching vo2max before fatigue / blowing up.
Stable physiology / heavy domain
Now lets take a trip to the other side of the border⌠when trained if I ride hard tempo for 90-120+ minutes (at about 85% ftp), my breathing is controlled but stable, my heart rate is stable, and eventually I tap out due to muscular and/or central nervous system fatigue. But I can keep training here and take it out to 3-5 hours. Or train by making it more intense and decrease time to around an hour (+/-) by raising the power to 90-95% ftp.
Finding the border / FTP
Now walk that in by increasing power from tempo, and decreasing power from your 6 (or 20) minute effort⌠Your FTP is somewhere between those efforts. We know that a properly paced 20-min effort is above FTP, will drain your anaerobic battery, and therefore unstable. So it should be somewhere in the 30-70 minute range.
When I look at a season filled with hard efforts and ability to ride about an hour at FTP, above FTP+20W was 10-min, and below FTP-20W was 90-min. Another season when I wasnât training long power, and only did a ~30-min long threshold effort, FTP+20W was 8-min, and FTP-20W was 42-min which was an artifact of not doing long enough efforts at threshold.
When looking at your data, context of training and hard racing (or hard group ride) efforts is required.
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Thanks for posting @david!
Hah, thanks @WindWarrior. âa little deepâ is the exact vibe Iâm going for 
Good summary of intensity zones/domains from an applied context! Exactly the idea I was going for talking about âtraining in zones, not at thresholdsâ. We know what sub-threshold feels like. We know what supra-threshold feels like. Those are the responses that matter. The sensations become more similar to each other and difficult to differentiate, the closer they get to each other. Somewhere in the middle of that ambiguous transitional state is our falsely-precise point-estimate power-value-to-the-watt FTP.
Get an estimate. Some tests are better than others for certain contexts. Start with that number to inform training targets. Adjust as required to the intended perceived effort. Feedback over time helps to improve our predictions & expectations. Train consistently. Improve. 
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@SpareCycles love the deep, keep doing it!
Exactly. Power inform feelings, develop your feelings and get better at training.
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I almost certain Jem , gonna do a Podcast with Koolie Moore in Empirical Cycling , and he is collecting Questions to Jem in instagram , if anyone is interested
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