Efficiency factor: interpretation question

So I’ve been looking at efficiency factor recently since it got baked into intervals.icu (for the uninitiated it’s normalized power divided by HR). Like aerobic decoupling it appears to be a measure of aerobic fitness, if you see higher EF during a ride then you’re aerobically adapted. I’ve been looking at my pettit workouts the past 5 weeks and they’ve all been 1.4, while my sweet spot intervals tend to be around 1.6-1.7. Now if I’m understanding correctly, EF doesn’t necessarily give insight into potential changes in FTP, but just base fitness? If so, then it makes sense why my EF is so steady since I’ve maintained aerobic fitness, even if not top end stuff, all year.

Anyhow, based on search results, this isn’t something that’s been discussed around here, so maybe we can get a good chat going and others can dig into this for their own riding and their aerobic fitness assessments.


I always enjoy digging up bookmarks and rereading Joe Friel’s blog:

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I think that is actually a bad example and article by Joe. Making any observations on improvement on two or three days of training period is obviously meaningless. Over longer period of time, say month and more, sure, you can see differences in your efficiency factor. On a day to day basis, there are so many factors, from external, like temperature, humidity, to internal - sleep quality over last night or several days, food eaten, workouts done before, etc that impact heart rate.

I would suggest reading another article by Joe, which, in my opinion, is much better representation of his knowledge on this topic.

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I’m not in agreement that is a bad example, however it might be taken out of context. This is what I’ve learned.

EF and decoupling are different metrics but related: https://www.trainingpeaks.com/blog/efficiency-factor-and-decoupling/

Decoupling is a metric for seeing improvements to aerobic endurance during base. The article you linked has good information about that, and how to use on long intervals to determine when you’ve established good enough aerobic endurance to move from base to another phase of training.

EF is about how efficiently you generate aerobic power, which changes over the course of a season. Its the topic of this thread and in The Cyclist’s Training Bible there is a functional aerobic threshold test. Joe suggests doing this test every 3-4 weeks, year round. So EF is used to track aerobic fitness over a season. And in the article I linked, EF can even shed some light on short-term trends.

As Joe suggests, for aerobic fitness over an entire season you should track EF. Use decoupling during base to determine when you have established enough aerobic endurance to move into next phase of training.

I guess what I am trying to stress and where Joe is providing bad example is that using workouts within short period time cannot be used with any confidence when determining whether there are any EF changes or not. Even workouts month apart might not be providing a good picture of any improvement or lack of it due to all factors that affect HR. I would suggest that one should always try to look at a bigger picture and longer trends then pay attention to any one or few workouts.

As Seiler rightfully points out in his presentations, one workout is probably 1/300 of workouts completed over year and obviously even lesser part of work completed over few years (that take for adaptations to fully occur). We should try not to make too much of assumptions while analyzing any short term changes because it might be misleading.

Coming back to EF and decoupling, I agree that those are great tools to measure changes of performance in time and also identify performance requirements required to be successful at certain levels. There is article analyzing Will Barta’s progress to WT level and his coach states that to be successful at u23 level rider has to have ability to a) Be able maintain 4w/kg for ~4hours with HR decoupling less than 5% b) After those ~4hours still be able to punch 20mins @5.5-5.8w/kg. That really gives some perspective on how good those guys are and that’s u23, at WT level fatigue resistance will be even higher.

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I’ve enjoyed looking at the EF numbers in intervals.icu as well. My EF numbers are similar to yours (1.4x for endurance rides and 1.6x for sweet spot rides). As an interesting observation from a 60 minute FTP test yesterday, my EF for the 60 minute interval was 1.45. I thought it showed that sweet spot work is also the sweet spot for power / HR efficiency whereas the relatively small increment to ride at threshold power had a pretty large increase in my HR and was less efficient.

My question regarding EF is: it is an objective number? Can we compare our EFs and brag about it?

Let´s say one cyclist “a” has a factor of 1.8, and another cyclist “b” has one of 1.4. Is “a” better than “b”?

My assumption is that this is not the case, since HR values are different for everyone. But perhaps it could work with percentage of MaxHR. i.e. 190 NP / 60% MaxHR = 317 and 200 NP/ 60%MaxHR = 333 .

Do I miss anything?

EF is an individualized number, meaning the only way to brag about it is to show that yours has improved relative to you.

maybe something convoluted like ΔHR reserve / MAP in W/beat/kg could be compared between individuals? But it’s probably better just to try and improve your own relative numbers, whatever those numbers are.