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Hi Joe,

Is it safe to go longer as long as there is no decoupling? (time permits)

I am using TrainingPeaks VCoach and it gave me Base 1 workouts to follow and I wanted to know if it's okay to increase the duration for those Z1-Z2 workouts as long as I don't see decoupling. The first week is going okay and recovery is looking good so far.



I think I meant no drop in power with same HR in Z1/Z2 or decoupling of 1%...

I am quite new to this so please forgive me if I am not using the terminology right...but I think I am getting there.

Joe Friel

Angela--You're doing great. Yes, it's ok to extend those workouts. No downside so long as excessive fatigue doesn't interfere with your training.


Hi Joe

I've just started my base 2 block, but what is worrying me at the moment is a vacation planned in march.
It is a business trip for 5 days where i am not able to train at any level (monday-friday). According to my ATP this week is a R&R week after my build 2 period. In the weekend following the weekend i am going to a gathering with my team. I am wondering how this will affect my hard earned fitness, because i am going to starting the tapering and peak weeks, right after this R&R week. Any advices on how i should handle this and how it will affect my fitness and form? My first A-priority race lies 2 weeks after this week :)
Thanks ;)


Is there a way of tracking this in a chart?



However I have a bit of controversy with a statement not related to the EF but more along the lines of muscle fibers and you stating, "cause type 2a muscles to take on the characteristics of type 1 muscles", in the first paragraph.

From my knowledge and readings, you can not convert type 2 muscle fibers to type 1 muscle fibers. The only change or % change that you can acquire between muscle fiber groups would be the 2b (or 2X) muscle fibers would express 2a characteristics.

Was curious if you have any research or evidence proving your statement is correct?

Joe Friel

Haakon_s - Not that I'm aware of but you could make one with an Excel spreadsheet.

Joe Friel

Mikkel - I don't know of anything you could do other than to train quite hard before the trip for a few days. There aren't any silver bullets for this.


Joe, did you consider that usually several consequent workouts cause a drop in average HRM given the same power output - due to fatigue. But as soon as you rest well, the HR rises up again. Can't this be the case here?

Joe Friel

Dylan--Yes, you're right. I've corrected the post. Some are proposing there is a type 2ab fiber which might help to explain this. Thanks for catching that.

Joe Friel

GA--Yes, it's possible that this is a factor. I've seen research that shows a decrease in HR over several days of fatigue-producing training (Mounier 2003). But I've never seen a study in which HR was kept the same to determine the affect on power/speed when fatigued over several days. I'm a bit skeptical that such a study would find an increase in output with fatigue as HR remains constant. There's still much to be learned about the relationship of fatigue, HR and performance.


I've always thought (based partly on your books) that it takes about a week before training resulted in positive performance changes, and then they would only be slight. your analysis seems to imply significant improvement within a few days. Could you please discuss how quickly the body responds to training? I know it would vary with period, age, previous fitness, etc. but an explanation for your specific case would be illuminating.

Maybe this is a topic deserving of a blog as I have never seen it addressed directly anywhere.


Hi Joe

I subscribe to Training Peaks and WKO+ and for now measure my running pa:hr, which typically is around 5%. Next year I will buy a power meter for my rdies. Where can I find my EF measure on TP's or WKO+?

Joe Friel

Hi Derek--EF is not on WKO yet. On TP.com if you select "Map and Graph" for a given run workout and then look on the ride side you'll find EF.

Joe Friel

Hi Blake--Yes, you're right. Good point. There are a couple of things going on here. I think improved technology (and how to apply it) is allowing us to view things we couldn't see before. And since what you saw in the table of workout results for this post occurred early in the year after some down time fitness was likely to change rapidly and therefore be more apparent. In other words, if I was in much better shape now the changes for this type of workout you see described here would not be as evident.


Another question: Could one use changes in EF to change FTP settings without testing? It would be wise to be conservative, but a rise of 5 watts at a given Z2 HR should translate to at least 5 watts at threshold, right?


I think you are making too much of a jump with the data you have presented. All the AeT scores are between 1.37 and 1.50 - there just isn't enough signal to know if we are looking at signal or noise. You have posited one plausible explanation, and though you did similar workouts and controlled for weather, breakfast, course, etc - there's just too much other extraneous stuff that I think you can't account for in this short data set with very little variation. To your credit, I think you know that and hint at it in your post. Perhaps this should be a "things I'm looking into post". Fitness gains and losses are always going to be very individual as well - there are "hard gainers" and "easy gainers".


Joe Friel

Blake--I don't believe you could draw any specific conclusions about what your FTP should be based on EF. But I believe you could tell if it was time to test again.


On Training Peaks, using a HR + GPS watch, I don't get EF data on the Map & Graph page. Like Derek, I see only the "Pa:HR" which seems to measure aerobic decoupling. Through 2 hours of a long run, the Pa:HR number is just under 1%, then it increases to 3% by 2:30, then it's just over 5% by the 3:10 mark.

As an aside, does this mean I meet your "under 5% decoupling" guideline, or should the entire run be under 5% even for 20+ mile runs?


Thanks. This is a timely post for me as I am a month into base training and it is my first season putting serious work into AeT and following an ATP. I have had some concern about what HR I should be riding at. According to the numbers I have come up with (following your books)I should be between 130 and 144 (with an AT of 163) but sometimes I feel like I am working harder than I should be for base training. This may be due to variations in PRE because of hectic work schedule. For point of comparison would you mind sharing your Aerobic Threshold?
(I realize one answer to the issue might be "your aerobic endurance is poor, but my comparative strength in endurance focused events (100 and 50 mile mtb) seems to suggests otherwise).

Chuck Tran

Hi Joe,
Your EF at the beginning and end of this period is essentially unchanged (1.41 and 1.42). Does that mean your aerobic endurance has not increased appreciably? Do you feel you have higher aerobic fitness now?

Joe Friel

Hey Chuck--That was my point--inconsistent training has not allowed me to make any gains as of the last such workout.

Joe Friel

LMG--Just ride in your low HR 2 zone (my system) which is roughly 30bpm +/-2bpm less than LTHR.

Joe Friel

DS--Your decoupling sounds good. I'll ask support at TrainingPeaks about EF for you.

Joe Friel

DS--I asked TP.com what the status of EF for running is. Here is the reply... "We are not calculating NGP in the file viewer yet, so I can not calculate EF for runs right now. We are working on NGP and rTSS in the graph for January and when it is there I will add EF."

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