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I think the question people are asking is this:

When I am riding along in HR Z2 or Z4, for example, why do I not always see myself producing power zone 2 or zone 4 efforts in that same interval? This occurs despite being on top of my heart rate and power zones, with testing for both happening in the recent past.

Mike Rehab

So when you are training to improve your power in a particular zone you are trying to alter the variable you are using to measure the training with?

Surely you can use your HR zones alongside power to provide a stable reference point?

I've read advice that when training with power you should "throw your HR monitor away". This would not appear to be good advice, as a steady state HR reading appears to be an unchanging variable to measure output against.

Am I missing something here?


Hallo Mr Friel,
I agree with your answer, actually on trainer power zone 2 don't match with Coggan's hr zone 2. But match with yours.
So I've found a significant difference in heart rate Z2 between Coggan and yours, Coggan suggest 69-83% of LT hr (linked with FTP zones), your Z2 start at 82% LHTR, so it's about where Coggan zone 2 ends.
What should I do if I want to train Z2 in winter?
I think this question should be asked also to Mr. Coggan.


my curiousity is more about why my heart ranges don't match exactly with my power ranges, specially at zone 2. If I use cogan's heart rate range for zone 2, I will consistenly be riding in upper power zone 2 and lower power zone 3. If i use training bible zone 2, I will be riding 100% in power zone 3. I have noticed this pattern several years in a row. My PFT is 280, and my LTHR is 167

Joe Friel

You'll have to make a decision, Lorenzo. You can't do both.

Joe Friel

Fulton--That's exactly what I explained in the post.

Joe Friel

Krystyna--Hmmm... That's what I explained in the blog post.


I've already made my decision Mr Friel, I think Coggan Hr zone 2 is widely underestimated. Training in that hr zone is easy as a walk with a girl. Your suggested Z2 is more challenging and is what i mean for consistent training.
Thanks again!

Richard Sterry

In my opinion, the answer is simple.

Heart Rate monitors measure Input (Energy In)

Power meters measure Output (Energy Out)

The ratio between the two is Efficency (Fitness)

This is why it is better to measure Power rather than Heart Rate.

Kyle Visin

I think most people understand (hopefully) that your power or pace zones will fluctuate throughout the season as your fitness changes while your HR Zones will stay fairly constant.

I believe the question that most people are asking is: "If you have a current accurate measurement (for example you just did a field test) for both your LTHR and Functional Threshold Power (cycling) or Pace (running) should your HR and power or pace zone match (or at least be relatively close)? If not, then why not?

I think the point of confusion is that many articles, people, coaches etc. Talk about Zone based training without specifying weather their talking about input (HR Zones) or output (power or pace zones). Hopefully this will change in the future.

Josh Knight

So is it better to train using input (HR) zones or output (Power or Pace) zones? It seems obvious to me that you want to test output, but does the same hold for training sessions?


I don't totally agree with you Richard because there are different pathways to make energy and oxygen is not involved in some of them. Therefore heart rate is not always a good measure for energy input.

My question for Joe is:
I often see that the heart rate at a given power output changes day to day. The day after hard training the HR will often be lower at a given PO and when you rest the HR will go up again. What is the reason for that? (more energy from glycoysis or CP-pathway? or are you just in better shape already?)
My solution is that on the recoverydays I use the powermeter to keep the PO down so I make sure I am not in Z3 when I should be training in Z2 or 1.

Hope it makes sense!

Jeff Reed

For me it makes sense that they won't always agree for a couple reasons.

1. Power should change over time with your fitness as the article above points out.

2. HR is known to vary per session based on how caffeinated you are, extreme heat, it's slow to respond, etc.

I take from #1 that I need to retest on a regular bases so that my power zones match my current fitness, but that because of both the reasons there will still be times that they don't match. The big question I was left with was "which one do I follow when they don't match?". The answer I came to is "follow power" provided my power zones are based on pretty current test results.

Joe, does that analysis sound about right?

Joe Friel

Jeff Reed - There is no "correct" way to do this. What I do is use HR when developing aerobic endurance in the early base period. After that I use power only.

Joe Friel

JOsh--As I told Jeff Reed: "There is no 'correct' way to do this. What I do is use HR when developing aerobic endurance in the early base period. After that I use power only."


Hi Joe, My local shop is offering a FTP building class twice a week and I attended today for the first time. As expected, my HR was jacked and it was a tough workout. I am currently in Build 1 and I know you recomend primarily Z2 training during this time. I'd really like to build my FTP, but is it too early to do so?

On a sidenote - I used your most recent book, Your Best Triathlon, this year and nailed all my goals for the year. THANK YOU! Really looking forward to 2012. Paul

Joe Friel

Søren - It doesn't always work that way (HR lower next day). There are many variables at play when we look at HR. Fatigue and changes in fitness are big ones, as you mentioned. For ex, I recently took 3 days off due to travel and my output-input ratio dropped by 4% primarily because HR rose. This was probably loss of fitness which has 3 components--VO2max, LT, economy. How much each of these changed, if at all, probably caused this.



What are your thoughts on HR vs. Power at eleveation? I find that power meters can get me into trouble at high elevations (7,000 plus). The zones we train in at 4500 feet are not the same as those zones at 8000 or 9000 feet--because we produce less power at elevation. I find that using the HR monitor to limit or structure intensity is a better tool for guiding my workout while climbing in the mountains. I also feel PE is a better option than power at hight elevation.

Your thoughts?

Joe Friel

Sam - We pretty much agree I believe. I just did an interview with Outside mag on this very topic. Not sure when it will appear.

Joe Friel

Paul--I suspect you meant Base 2 not Build 2. You most certainly should be working on FTP then. It just depends on what you mean by "working on" relative to your next A race.



I've observed the same phenomenon (little change in HR zones, particularly compared to power changes over the course of the year). How do we reconcile this with the adage that LT is "very trainable"? I've been working with that starting premise - is it not true?

Joe Friel

Lisa--Output is very trainable. Input is not. You just get faster; it doesn't feel harder.


Hate to dig up an old blog post. I've read the Triathletes Training bible(Great Book) and have a good base training the last four years. For 2013 I'm re-evaluating all my HR Zones and Power Zones. Using data from 2012 I've collected, my LTHR looks to average 150bpm from several solo efforts either Running or Cycling. With 5-10min warmup would it be fine to use 8mi TT runs to further Tune LTHR and use the Power Output to calculate Power Zones, or would the Effort need to be at least 30min or longer.

Joe Friel

Thrash155--The two main ways of determining FTP are Coggan's 20min test and my 30min test. Your HR for the last 20 minutes of my 30min test is a good predictor of LTHR. I can't speak for Coggan's test as I've never used it.

Harald Riisnas

Hi Joe.
I have been injured for more or less two years. I started my training some weeks ago, my back finally seems to work as it should. When i train in powerzone 1, my heartrate tells me i am in high zone 2, and after some time even in heartratezone 3. I guess my low aerobic endurance is the explanation. If I understand your principles correct, it means i should stick to the heartratemonitor when building my aerobic endurance, and focus on aeobic endurance only?

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