Power is not definitive, it is a factor, the same as HR

Tonight’s session was borrowed from a mate who subscribes to the alternative online tool.

It was holding tempo for 1 hr with 5 min +10 w then 5 min back down again repeating 6 times.

I was aiming to be -20 rpm cadence, self selecting ave cadence and +20 rpm cadence.

So giving this simple numbers

Interval 1 at 200w at 75 rpm
Interval 2 at 210w at 95 rpm
Interval 3 at 200w at 115 rpm
Interval 4 at 210w at 75 rpm
" 5 at 200w at 95rpm
" 6 at 210w at 115 rpm
" 7 at 200w at 75 rpm
" 8 at 210w at 95 rpm
" 10 at 200w at 115 rpm
" 11 at 210w at 75rpm
" 12 at 200w at 95rpm

SO…the my HR was lower across both power outputs when the cadence was lower/est and conversely my HR was highest when my cadence was high.

My point is if the power is hard drop your cadence I recall a podcast about efficiency - after a deep dive the synopsis was - aerobically to be efficient drop your cadence to achieve maximum power raise your cadence.

Feels like it brings power as the definitive metric into question. And that is pretty much what Inigo San Millan says - HR is the physiological response so use that not power.

Any thoughts?

PS I am aware this is N=1 so I’d be interested in your findings from hours in the pain caves of the world.

:+1: :+1: :+1:


My 2 pence…

Watts are Watts (definitive metric) but heart rate varies with cadence :man_shrugging:


Yeah, I think of it like this:

  • Power = Objective and consistent value over time = Concrete floor
  • Heart Rate = Subjective and variable over time & other influences = Sand floor

I know which one I would use as a repeat reference (the stable and repeatable one).

  • That said, I don’t discard HR, but use it as a secondary (that’s interesting) kind of metric. A bit like RPE, 200w may feel really different from one day to the next, for a host of reasons.
  • So, despite power being the most consistent over time, it’s not perfect when considering the flabby machine connected to it is full of variability :stuck_out_tongue:

And yes, the simple observance that at the same power:

  • Lower Cadence = Lower relative HR
  • Higher Cadence = Higher relative HR

Again, interesting and might be leveraged. But in a vacuum, they don’t mean that much.

  • Looking at your needs in events and considering how to apply the range of cadence within different power and effort ranges is something each rider must consider. There is no absolute for any rider or event type.

I hear what you are saying, and not forgetting lag, but if I’m training at VO2 or below (no AC or NM as HR doesn’t have time to respond in a meaningful way) then the physiological responses may not be happening or maybe more extreme than expected if the cadence is lower or higher and therefore the physiological response and signalling is not what the training plan was aiming to create. EG doing a VO2 workout at a low cadence actually creates maybe a Threshold or Tempo response.

Perhaps HR will prove to be more useful at VO2 and below and above VO2 PM .

I suppose what I’m saying is that power is not definitive and can be bamboozled and as Chad says the flabby random performance generator confounds it too, just perhaps the adulation power is given needs to be qualified.

The laws of thermodynamics would suggest otherwise :stuck_out_tongue:


Not 100% sure but sounds like you are trying to reconcile strain and stress? Or work output (objective) and physiological phenomena (also objective but not strictly tied to work output)?

I don’t want to parse or nitpick but both are definitive. Your heart is beating those many beats and your body is putting out that much power.

The conclusions you might draw from either one are certainly not definitive.

Too bad we don’t get stroke volume. Then you could draw more (but still not completely) definitive conclusions.

The power you produce is objective. Your FTP, on a given day, is not though - it depends on how much stress you had recently, how well you recovered, how long ago you actually had your last FTP test:) and so on.

Some companies, like Garmin, are getting real good at establishing a correlation between power you produce and HR - which to me looks like a great use case of getting somewhat reliable insights from two unreliable sources of data.


There is definitely a most efficient cadence for power output, or at least currently conditioned. Hold 90% FTP for 10 min at comfortable/self selected cadence (eg. 95rpm x 10 min = 950 “reps”). Now adjust resistance and then hold 90% FTP for 10 min at 120% of your comfortable cadence (114rpm x 10 minutes = 1140 “reps”). In this example even if every “rep” is “lighter”, you’re fitting 190 more “reps” into the same time frame. The faster work/turnover rate will drive HR up. How much above self selected cadence you’d have to go to experience visible inefficiency might vary person to person and even within training/conditioning.

Power is by definition, work over time. In cycling, your cadence is the time factor in the equation. There are more than one ways to make 250 watts.

Power can be broken into the physics equation of
Force x distance / time

On a bike, the force is how hard you are pushing the pedals, the distance is the lever created by your crank or your crank length, and the time is you cadence or revolutions per minute.

You can hit a power target by pushing harder at lower rpm or vice versa.

Power is simply another metric, just like heart rate, or cadence. Power is the best metric when comparing efforts because it is very well defined and never changes, a watt is always a watt.

Athletes need to consider HR as the human factor and cadence as a terrain factor.

You are correct that power is a factor but you need to know yourself to decide what cadence is appropriate for your physiology and remember that HR is the human factor and helps to reveal your performance on that particular day.

Great topic, honestly, it’s crazy how much time I spend thinking about these three metrics every workout!

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The issue is we use TrainerRoad to train, it’s not Zwift games or performing out on the track or road in a race or a sportive. Therefore to train we need to optimise effort in relation to the desired physiological signalling and impact. Failing to do so is analogous with having an incorrect FTP - we think we’re in Z1 but because of FTP was somehow over reading at the FTP test we are actually into Z2 physiologically which fundamentally that is all that really matters as while laws of physics are fairly strict the laws of physiology are very subjective and individual.

And whilst we could say TR is a one size fits all “solution” perhaps it should consider the impact and implications of other demonstrable, measurable and recordable metrics. Those that say but “Power is Power” are actually missing another valuable metric.

This is supported by the fact we all have different power curves too, so naturally individually we are predisposed to certain ranges and capabilities. For example if my Endurance capability is exceptional but my VO2 is the exact opposite when I am at 75% FTP I may only be midway through my Endurance Zone rather than at the upper end. However equally so my VO2 range may actually only be 103%-114% FTP. (EDIT - I met with Jamie Pringle at Boardman’s High Performance Centre and in a presentation he said across the power zones nearly everyone of us has an elite level performance - be that Z2, Z3…Z7 but sadly only the pro’s have it across many or marginally below across all zones).

This thinking has been bubbling away for a few years. I think power is taken to be absolute and it’s not (in response to physiology not physics @stevemz) . It can only be a contributing measure a significant one but whilst thinking “power is power” it could be very wrong; it could be better as part of suite (that is perhaps too sophisticated for an online mass market service offering) and I suppose I’d ask for that honesty from all the training systems.

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Just because your heart rate doesn’t respond, doesn’t mean you still aren’t elliciting the same systemic response based on the power output. RPE could be a similar metric even though it is subjective. Just because the RPE of a ride wasn’t as high, doesn’t mean it wasn’t as hard as another ride that felt harder. Heart rate varies based on a lot of things and you can’t always control them. If you drank some coffee before the ride, your heart rate may go up, which would mean you might tone down your cadence for the wrong reason.

Oh yes I get different HR is not absolute, but these are relative and within the same time/fitness/hydration test so a lower HR is a lower HR that elicits lower physiological responses because my HR is a rough measure of that.

but you are missing the point. for the fact as you say heart rate isn’t absolute, the phenomena that the heart rate is lower, does not mean the physiological response is less. Yes your body did not raise your heart rate as high, but that doesn’t mean everything else was less.

I’ll add, I would think most would see the lower heart rate response as advantageous as it likely means the RPE is less and thus the quality of the workout better at the target power, not worse.


I think your choice of words is why you’re getting disagreement.

Power is a definitive, internationally recognised measure of output, and importantly for cyclists an objective and measurable one.

Heart rate is not those things. It’s measurable but subjective.

I use power to define my training, power zones to describe the impact on my aerobic endurance etc, and my heart rate to describe the impact it had on my cardiovascular system.


There is nothing you can do, literally nothing, that can change the mechanical work energy required to move yourself up a 1 mile hill at 6% grade. Assuming variables like weight, wind and tire pressure, etc are held constant, the work required to get you up that hill will not change. Power is just another description of mechanical work (i.e. you can always convert kJ to W provided you know the time period)

The physiological response from your body will change depending on how you ride up hill depending on pace, temperature, cadence, state of hydration, state of fast, etc.

If you are trying to say that there is variation in individual ability to produce power over time periods, then yes, that is true, but that doesnt make power less important, it makes it more important.

Let’s try putting this a different way:

What problem are you having that isn’t being solved by power right now?


When you cycle, it takes energy to just spin your legs.

Think of it this way: If you pedal with no resistance (think of no chain) at 150rpm, how long do you think you could keep that up? Mechanical power is zero. So you should be able to keep going all day, right? Well, clearly not.

So it’s no surprise that at higher cadence HR is higher, because you are expending more energy. This is well documented in studies - lower cadence is more oxygen efficient. Higher cadences less so.

There’s a separate reason why pros ride at higher cadence to do with muscle fiber recruitment and fatigue resistance, but I’ll leave that for a separate discussion.

The answer is use both (and RPE, in addition to HR).

Back to my exaggerated example, if you had to ride at 200W for an hour, would you chose to ride at 150rpm or, say, 90 rpm?

The power is the same, so if you just looked at power, you’d say it doesn’t matter what cadence you ride at. 200W is 200W. Speed, time, etc will be the same.

But we all know that riding at 150rpm is going to be a lot harder, so we’d ride at 90 instead. HR tells you that, as would RPE.

Point is, no need to be dogmatic about “power is all that matters” or “heart rate (or RPE) is all that matters”. They each have their merits, and makes sense to take both into account appropriately.


I’m not suggesting power is now entirely debunked and was the Emperor’s new clothes. But I do think it should be used in conjunction with other metrics.

And yes I understand that speed up a 1 mile 6% hill (assuming all other factors are constant) is dictated entirely by power.

My point is: If we are using Power to train, as TR is entirely power based I assume we all are happy with that, then it is not a complete picture and lacks the subtly of the real life implications and as such they should be mentioned, not discounted as a metric as HR is. HR indicates the physiological state and that is surely worth considering when finding training zones or objectives.

We’re all here and paying our subs as we are believers in power, but I think we should consider other factors too, HR (and RPE) being the most obvious and easiest to asses.

(And before anyone says “ah yes but HR is variable” we all agree that power output is affected by cadence, perceived pain is affected by pain killers and or caffeine or mood or motivation and music so out FTP tests can be “gamed”)

  • Best not to assume.
  • Plenty of us consider HR, RPE and other factors in our training.
  • TR is a foundation and many people choose to supplement it as they see fit.
  • Sure, just like many of us have already accepted.
  • But we also made note (and you accept) that it is subjective and variable, so it must be considered with the wishy-washy nature of a metric that is not absolute or objective.
  • Agreed, as others have as well.
  • For me and others, it is secondary (to power) and supplemental, but still worthy of a look.

And with heat, sleep, previous days, how much water you consumed, and a billion other things


Yes, I think most on this thread would agree with that statement :+1: - but not the thread title :slight_smile: