When should you be riding by HR instead of Power and what can you learn from a HRM when you're riding by Power?

  • If you can use both Commented Nov 6, 2017 at 20:54

5 Answers 5


There is only one occasion I would consider use of HRM has priority over a power meter (or indeed no monitor at all and simply using perceived exertion), i.e. your doctor or cardiologist has specifically requested you not exceed a certain HR.

Otherwise there is no time that, if you have a power meter available, using an HRM trumps using a power meter.

One of the problems in answering the question is it's considering the quite narrow paradigm of training by power, in the manner that one might have used HR previously.

There is far more to training with power than is ever possible with a HR monitor. But that is for another discussion.

So if we are to consider only the narrow paradigm of using power meter to set training levels and to guide intensity of effort while riding, then there is very little extra to be gained from HR data. There are many who believe they can read the HR tea leaves but there is very little valid actionable intelligence to be gained, and if anything the risk is high that it will be misleading or poorly interpreted.

HR response is naturally variable in a day to day sense, and varies depending on many factors other than how hard you happen to be riding. Unfortunately the impacts of those factors are themselves quite variable and one cannot reliably parse them out by looking at HR or HR:power ratios. e.g. fatigue can result in either an elevated or a depressed HR response for a given power output.

If your HR is a little elevated or depressed on any given day, then provided you are banging out the power OK it really doesn't matter all that much. If it's significantly varied though, then it's just as likely that your level of perceived exertion is also telling you something is up and/or you are simply not able to sustain the power level/range that you might ordinarily expect, or perhaps you realise you can go somewhat harder. HR does not add much to the combination of power and level of perceived exertion.

HR has its uses if you are not using a power meter but its utility is confined to primarily guiding sub-threshold mostly quasi-steady state intensity. It's pretty much useless for guiding any supra threshold or highly variable efforts since the lag in HR response is such that most such efforts are nearly or completely over before one's HR actually reaches such a nominal intensity level.

As power climbs towards threshold, one also need to be aware of cardiac drift, the perfectly normal gradual rise in HR while riding at one's metabolic control limit (threshold). If you attempted to pace such an effort with HR and did not account for this, it's highly likely your effort would be poorly paced (started too hard and power will fade throughout).

Below is an image showing typical HR response during interval efforts at around threshold power level and shorter harder efforts that are close to eliciting a state of VO2max. Note the response lag time, and how little time during the harder efforts HR actually spends in that nominal maximal aerobic "zone":

enter image description here

  • 1
    @AzulShiva - In a short interval, HR is an unreliable measure of effort as nicely shown by Alex. For example, I found being rested made my HR more labile, resulting result in a higher HR for a given effort. Where you more rested coming into the first interval?
    – Rider_X
    Commented Sep 23, 2016 at 17:02
  • 3
    +1 for a clear summary of why HR can be difficult to interpret . That said, I think you are brush off monitoring fatigue too much. Changes in resting HR, differences in the association between perceived effort and HR, ability to elevate the heart rate and max recorded HR in a all out race effort (e.g., road race sprint) can all provide insight into fatigue status. While power perceived effort and power can be used to similar effects, it is nice to have multiple lines of evidence that shows it you are not simply lacking motivation, but are in fact fatigued and need to rest.
    – Rider_X
    Commented Sep 23, 2016 at 17:23
  • 2
    I understand, however when you have power data and PE it is also telling you these things (making HR essentially redundant), as well as enabling far more insight to be gained into actual training stress and cumulative training loads over shorter and longer periods. This is where the paradigms of training by HR and training with power begin to diverge. As to keeping an eye on resting HR, yes if it's significantly elevated it can be a sign of a few things (but what is often not evident until later). That said, one does not need a HRM for that, just a watch and your finger on your pulse. Commented Sep 24, 2016 at 3:22
  • 1
    With current technology, HRMs only tell you how fast the heart is beating. They don't tell you stroke volume so you can't get cardiac output. They don't tell you how much oxygen your current blood state can carry, or how much is being used. This is why cardiologists need a lot more information than pulse rate in order to know what is happenning in your circulatory system. HR turns out to be a very limited piece of information, affected by many other variables. That's why it can be difficult to interpret -- and difficult to use to guide ride effort.
    – R. Chung
    Commented Sep 24, 2016 at 16:17
  • 2
    Another source of noise when interpreting HR: dehydration can cause your HR to rise. If you're on a long ride and not drinking enough your HR can trend up while your power output trends down. (And, BTW: great answer, @AlexSimmons!)
    – keithmo
    Commented Sep 25, 2016 at 18:09

You can tell when you are knackered.

Power indicates your actual output. With a baseline of previous power and HR data, you can establish a model for what you should be able to do. When your numbers start to fall way outside your model/baseline (you normally produce 250W at 80% of your max heartrate, but now you are only producing 200W at 85% or 90% of your max heart rate) it might be time to do something about it (check hydration, calories or just end training for the day). Additionally in off training times your resting heart rate can be looked at as an indicator for how well recovered you are.

Power output is a finite number that is extremely useful because comparisons can be made directly across riders. However, your own stats bio metrics are more useful to you as an individual because they can help guide your training and prevent you from overtraining, help show your individual improvement, and let you know when you are recovered and can accept an increased training load.

  • 2
    Also it's useful for training certain effort zones: endurance, tempo, lactate threshold, etc. In those cases, you don't care what your power output is — you're trying to increase your power output at a particular left of effort, and the best way to measure effort is heart rate. Commented Sep 20, 2016 at 23:48
  • So, to summarize, training zones and exhaustion are pretty much the only 2 reasons?
    – AzulShiva
    Commented Sep 21, 2016 at 6:58
  • "Power output is a finite number" – speak for yourself :-) Commented Sep 21, 2016 at 13:32
  • 1
    @AzulShiva No. Those are the two BIG reasons. If your training regimen isn't taking those things into account, you are wasting your time. Commented Sep 21, 2016 at 15:06
  • That's a bit rash no? Eddy Merckx had 0 tech on his hands and he did just fine... but I get your point and I'll look into it. I have my zones set obviously but I'm not relying on my heart rate/Power ratio to do my recovery yet.
    – AzulShiva
    Commented Sep 23, 2016 at 7:34

A heart rate monitor (HRM) measures cardiovascular system effort, while power measures muscular system effort. When averaged over long periods of time the two are typically highly correlated, they can also diverge depending on the circumstances, for example in a sprint your HR will lag behind your effort or your HR for a given power effort can vary by fatigue level and hydration level.

Looking into the interplay between the two can give you a lot of insight into performance. For example, using a higher cadence will elicit a higher heart rate, but might let you sustain a higher power output, or let you keep your legs "fresher" for a given power output. (By "fresher" using primarily type 1 fibers instead of type 1 + type 2 as type 2 are best "saved" for short power bursts such as sprints or pursuits). By experimenting you can start to learn how to get the best performance. While power ultimate is what wins races, your muscular system is supported by your cardiovascular system, the two need to be considered in tandem.

HRM is also good for nailing down your heart rate training zones. Most training material will still refer to these zones. You can use an HRM to accurately determine your zones if get good estimates of your max heart rate (all out effort in a race) and resting heart rate (when you wake up). If you keep a long time series of data this should be easy to determine. DO NOT use that horrible 220-age formula for your max (the 95% confidence interval on that relationship is something like +/- 30 bpm), it can only be reliably estimated under extremely intense exercise and shouldn't be attempted by people with any sort of pre-existing heart condition or untrained. Once you have accurate estimates of your HR zones, you can for example know with pretty good certainty that hard effort you thought was anaerobic, actually wasn't, therefore there was more power that could be teased out.

Finally, as pointed out by @SuspendedUser HR can be good at monitoring fatigue and general health (e.g., hydration levels). If you are not cannot maintain a particular power for heart rate zone this could be an indication that something is up. General long term training fatigue is probably best measured by max heart rate in all out effort. If you went as hard as you could but didn't hit your max there is a good chance you are over-trained. Resting heart rate will also elevate under fatigue.

  • 1
    +1 For 220 - age not being entirely accurate (mine is actually only 6 bpm above what the formula predicts). However, I will say it isn't horrible per se, just not as accurate as a simple to do test. It may be a good starting point for someone in extremely poor shape that can't even manage a short sprint. However, after a couple weeks of training, it should be abandoned for the results of a test. Personally I can't/haven't hit mine cycling in a long time. I've hit it several times at a full sprint running. Commented Sep 21, 2016 at 4:24
  • 1
    @SuspendedUser I believe it was based on a sample size on n=5, with all the subjects were obese smokers. It was intended as a guideline for doctors not to kill very out of shape individuals when they started an exercise regime. Polar used it as a cheap way to set zones on their early HRMs and it had lived on ever since.
    – Rider_X
    Commented Sep 21, 2016 at 4:29
  • 1
    The guy who came up with the 220-age formula explained it here.
    – R. Chung
    Commented Sep 21, 2016 at 23:24
  • Comments are not for extended discussion; the majority of this conversation has been moved to chat.
    – Gary.Ray
    Commented Sep 30, 2016 at 12:49

HRM's tend to be more affordable than PM's and you don't need to remove them from one bike if you train with different bikes.

If you don't know your LTHR and FTP, I think you're better off using a HRM if you must pick one or the other.

A HRM can give us an idea of when to back off. For example, elevated core temperatures can increase our heart rates. Recently, there's articles warning against extreme endurance exercises. It may be a healthy choice to avoid overworking our hearts by proper cooling or backing off. Experts seem to agree that we should limit our HR to 85% of its max.

Having a fan while turbo training seemed to decrease my HR during sweet spot intervals from around 90 to 80 percent of my max HR. Antelope - TrainerRoad Oct 20 2017 without a fan.

Tunnabora - TrainerRoad Oct 31 2017 with a fan

  • It's been proven that exercising under hot temperatures improves training results. As you can see your body is less efficient at high temperatures so practicing exactly that is a good idea. Lose the fan. Please provide links to those articles.
    – AzulShiva
    Commented Nov 6, 2017 at 12:30
  • There's many articles about temperatures affecting heart rate. You can look up the key words cardiac drift. How do we know whether it's heat acclimation or exercise at high temperatures that improves training? Saunas can improve exercise performance. Riding outdoors is similar to using a fan in terms of cooling. Heat acclimation increases plasma volume and cardiac output. ncbi.nlm.nih.gov/pubmed/20724560
    – Brian
    Commented Nov 7, 2017 at 0:45
  • Do a 5min max effort at 10 degrees celsius. Then try and do the same watts at 35 degrees. It's not possible. Heat acclimation or not. Also, at high temperatures oxygen density is lower so you'll get the same effect as at high altitude.
    – AzulShiva
    Commented Nov 7, 2017 at 14:34
  • At least in theory. You can see they put out 2-3 more watts so the title is bogus. ncbi.nlm.nih.gov/pubmed/25943678
    – AzulShiva
    Commented Nov 7, 2017 at 14:38
  • Maybe for light workouts, we can safely lose the fan. Note that for every 1 watt on a trainer, about 3 watts is heat in the body. If our FTP is high and we're racing on Zwift, you can see how important cooling is.
    – Brian
    Commented Nov 20, 2017 at 5:17

I use an HRM with my PM when training indoors to monitor my cooling and hydration strategy.

  • 1
    Welcome to Bicycles. Please take the tour so that you can make best use of the site. At present this answer lacks detail, so please edit it to explain how you use it to monitor cooling and hydration.
    – andy256
    Commented Sep 21, 2016 at 0:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.