Should Heart Rate and Power Zones Agree?

A couple of days ago I received an email question from an athlete. He explained that his heart rate and power zones don’t agree and that there seems to be a two-zone separation with the power zones higher than the heart rate zones. I took this to mean that when he was in power zone 4 his heart rate was in zone 2. I get this question a lot, but it’s not always this relationship. Sometimes the athlete tells me that his or her heart rate zone is higher than the power zone.

 

I know of no research on anything like this. All I’ve got to go on is my experience in coaching athletes with power meters and heart rate monitors, including myself, for the past 10 to 12 years. I require all of the athletes I coach to have both devices and use them for every workout. I only coach four athletes a year, but they are a serious group and train a lot. So I’ve seen a lot of data over the years.

 

But before getting into what I’ve found regarding this athlete’s dilemma, let me explain the zones I use. The heart rate zones I use are found in tables in my books: The Cyclist’s Training Bible, The Triathlete’s Training Bible, The Mountain Biker’s Training Bible and Total Heart Rate Training. For power zones I follow Dr. Andy Coggan’s as described in his and Hunter Allen’s excellent book, Training and Racing With a Power Meter. His zones are based on functional threshold power (FTP) which is similar to lactate threshold or anaerobic threshold. It’s the power you can sustain for an hour in a race. Coggan’s zones are as follows.

 

PZ1 <55% of FTP

PZ2 56-75% of FTP

PZ3 76-90% of FTP

PZ4 91-105% of FTP

PZ5 106-120% of FTP

PZ6 121-150% of FTP

PZ7 >150% of FTP

 

If you’re not using these two sets of zones for heart rate and power then what I’m about to explain may well not apply to you at all. Please bear that in mind if you have a question to post here. I am not familiar with other zone systems so can’t comment on why yours don’t agree in that case. In fact, you’d be amazed at what I don’t know about other coaches and their methodologies. I have a hard enough time just keeping up with stuff that is critical to my growth as a coach. There simply isn’t enough time to know what others are doing and why. I’m pointing this out upfront because I get lots of questions assuming I know things. Best not to do that if you have a question.

 

So now let’s get back to the issue at hand: Why don’t the heart rate and power zones always agree?

 

I should start by saying I have never had an athlete whose power and heart rate zones were exactly the same all the time. But for most the zones have overlapped by quite a bit. So, for example, when one of these athletes with overlapping zones is in high zone 2 heart rate, he or she may be in low zone 3 power. That’s quite common.

 

Having only a small overlap is not unusual either. There may only be a narrow range in which the zones overlap. Having a complete one-zone gap is also not unusual. A two-zone gap, as the questioner said he experienced, is unusual but not unheard of.

 

Testing is a key variable here. As mentioned, it’s necessary to know your FTP in order to set up power zones. The same goes for finding lactate threshold heart rate (LTHR) in order to set up your heart rate zones. If the tests to establish FTP and LTHR are remiss then the zones will not be accurate and unusual gaps are likely. So the first issue is that self-testing must be accurate. The more times you do the FTP and LTHR tests the more accurate the zones will become.

 

His issue was that his heart rate zones were low relative to his power zones. That’s actually a good problem to have at this time of year. The most likely reason for this is that aerobic fitness is very high and exceeds muscular fitness. So the heart does not have to beat as fast to provide oxygen to the muscles. This implies the need to improve one’s power.

 

Having a high heart rate when power is low is a less attractive problem to have and is more likely to occur when aerobic fitness is sub-par. This also may be the situation after an illness or when highly fatigued. It may even be an indicator of overreaching and is likely to show up after a lengthy block of crash training. If so, rest is the most likely solution. But it could also be that more aerobic training is needed.

 

The bottom line here is that it’s not unusual to have some discrepancy between heart rate and power zones. It may even be fairly common with both sets of zones fluctuating due to the constantly changing interplay of fitness and fatigue. However, heart rate is likely to change the least, I believe. Power is much more sensitive to training.

 

I wish I could give you hard data to back up my beliefs here, but there are none. I continue to monitor such situations (I currently have one going with an athlete I coach which is probably related to extended overreaching). If I learn more on this topic I’ll certainly post it.

Comments

[Matt]

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.

[Chris]

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!)

Thanks

[Robnfl]

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.

[Jonny]

Joe,
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?

[lawrence]

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?

Paul

[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.

Paul

[Glenn]

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.

[Martin]

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.

[Andrew]

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:
http://itunes.apple.com/no/app/bike-meter/id382430416?mt=8

[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 :)