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Great article - thank you!

I assume that the same could be said of pace-derived zones? I'm comparing HR and pace results from a 30-minute LTHR test for running.

Paul Smernicki

This is a perfectly timed post,as I have been considering this question of my own training recently. In my case I am pretty sure it is down to testing protocol but your insight on this is really valuable. I have commited to a big goal for next season and given that there is little I can do to increase my available training hours, more accurate and better use of testing is one of the areas I have identified as potentially adding gains to my overall performance.
Keept the good stuff coming Coach Joe!

Joe Friel

Hi Matt--Yes, pace is similar to power in this regard.


I would be very interested in what data you gather to this topic. I am in the same boat as this article's question poser. I often experience z2 HR when in z4 power....my HR zone will get close to z3 after holding this power z4 for some time.
I do the cp30 test on a computrainer to create my power zones using your zone calculators in TP.

Perhaps a cp60 test would be more accurate (though I can't imagine doing the test for twice as long!)



Joe, Great article. You didn't mention that external forces, such as humidity and temperature have an affect on heart rate and power. During hard training rides and races in high heat or humidity I can see as much as a 10% drop in sustainable power along with a corresponding increase in heart rate, completely skewing the relationship between heart rate zones and power zones.


What is the proper way to calculate % of HR zones? Do i calculate it from the actual HR number or do i subtract out resting HR? The difference between the two is significant. Power goes from 0 up, HR goes from resting up, could this be the cause for the confusion?


So does that mean if you notice a drop in power relative to HR, say due to training volume, then you should follow HR for that session or should you continue to try and push your power zone?

Paul F

Hi Joe,

Great topic.

What I find I experience with my athletes is that when they are in ther heaviest periods of training, their HR's seem to stay low. I quite often get the "I just couldn't get my HR up today but my speed/power and RPE felt great"
Could this possibly be a sign of cardio fatigue as opposed to muscular fatigue and and early warning signs of muscular fatigue to follow?


Joe Friel

Paul--I've never heard of the heart expeiencing fatigue. that's why it uses lactate as a fuel source duing exercise.

Joe Friel

Lawrence--I can't answer that. Way too may 'it depends.'

Joe Friel

Jonny--You need to read one of my books on setting zones.

Joe Friel

Robnfl-And diet and psychological stress and recovery and altitude and...

Paul F

G'day Joe,

Isn't the heart just another big muscle, which would be subject to stress and consequently fatigue?

If the heart doesn't get tired, wouldn't we just be able to keep pumping blood at XXX HR and never stop?

I was under the impression that all of our systems undergo stress and fatigue which results in periods of rest, growth and adaptation.

Just to throw it out there another way, if we go out and perform a LTHR test (ie max effort for 1hr) are we limited at a muscular level, if so, is it then possible to maintain LTHR for much longer periods then just 1hr? at what point does the cardio system fatigue and slow us down?

Just trying to get my head around this.



I have found early in a ride my power zones are up to 2 zones higher than my HR zones. But as the ride goes on they come into alignment. I figure this is because I'm alot more rested early in the ride. So I have figure alot of the time its fatigue related. Power/Pace is constant where HR/RPE are affected by rest/recovery.

One thing that never changes though is when I'm climbing sitting I can be at the top of Z2 HR but still in Z4 power for 5-10mins with no problems.


Having had the same situation I think there is another factor to bear in mind. If this happens one thing to do is carry out some semi-blind or blind rides. So do some drills where you can see power but not HR, HR but not power and some where you just go on RPE alone.

This will help avoid one risk of training with power which is that your brain bases the perceived effort on the wattage numbers it sees on the CPU as much as the physiological feedback its getting.

In this vein I think I recall some work on this which showed that giving subjects incorrect feedback on speed resulted in them going faster in reality.

And I know from my own experience the key factor in me doing a century under 4 hours was to deliberately set my ride computer to slightly under record speed then pace just by focusing on keeping the speedo at the crucial 25.0 mph mark. Worked like a dream, I was oblivious to all other measure like power/real time and came in 5 minutes under target.


I would expect Joe's HR zones to not correlate to Coggan's power zones. If you compare Coggan's HR ranges to Coggan's Power zones you are more likely to get a closer relationship.

In my sample of n=1, I found this to be true. The HR does move around quite a bit depending on the factors previously discussed - but I have found the averages over time, for similar conditions to be closely correlated.

Gerhard Sletten

Hi Joe

I have made an Iphone app where the athlete can add his Functional Threshold Power (FTPw) and Lactate Threshold Heart Rate (LTHR) and will calculate the training zones.

Its free and available in AppStore as Bike Meter:

cmon myname

Paul: to answer your last question, in races my "LTHR" somehow moves up a bit (i.e. higher than it would be in training), so, I've been able to average very close to this HR for over 2 hours easily. this shows that the limitation isn't the heart muscle, it is something else. I don't know when it would get tired and I'm not sure I want to know :)

Joe Friel

Jim--Depends on the purpose of the workout. Heart rate is s good gauge for aerobic threshold workouts, power meter for all others.

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