Heart Rate VS. Power for Cycling Training (Science based coach explains...)

Heart rate or power—what's the better tool for cycling training? In this episode, we break down the pros and cons of both, and why we believe power is the more practical, reliable metric for most cyclists. From pacing your efforts to tracking progress, we explain how power takes the guesswork out of training and why heart rate still has its place—just not as your primary guide.

Full Transcript:

Cam Nicholls (00:00):

Welcome back to the RCA podcast, where today I'm joined again by the RCAs data nerd Ben Treble. And today we're going to be talking about zone two. Should you be following power or should you be following heart rate or should you be following both? And if you're following both, how does that actually work when one's staying in a straight line, the other one's going all over the place. So Ben, what's your answer?

Ben Treble (00:27):

I prefer to use power both. I like definitely both, but I would start with power.

Cam Nicholls (00:34):

Okay, that's a bit controversial, especially somebody who loves science and digs into all the papers. Why do you prefer power? Is that a scientific, I feel like this is maybe the first time you're going more on the practical side than the scientific side. Is that fair to say?

Ben Treble (00:51):

Yeah.

Cam Nicholls (00:53):

Oh, there you go. So why is that? Tell us why

Ben Treble (00:56):

Heart rate for everyone listening, maybe there's some basics. Heart rate is an internal measure of our stress, which is fantastic because we have to listen to that and it's a metric we should always be accounting for and learning to listen to. Power is an external metrics, so in that respect, power is very reliable. Power doesn't discriminate when you are tired. Power doesn't discriminate when it's windy or cold. You are fatigued. 300 watts will always be 300 watts provided

Cam Nicholls (01:29):

You calibrated.

Ben Treble (01:30):

Yeah, provided you've got a good power meter .... The heart rate though, whilst it's a very good internal measure and scientifically you'd probably say a better measure for zone two in some respects because there is drift to account for especially in longer rides. My challenge with heart rate for zone two rides is simply it's harder to follow because your heart rate takes time to respond to the work. And how do you respond to that? If you suddenly see your heart rate has slowly crept up 15 beats throughout the ride, how much do you decrease your intensity to try and drop it? Because you most likely will drop it too much. Your heart rate takes time for this up and down, right? The response of it equally comparing workout to workout gets difficult because how do you account for all these other external stresses that your heart accounts for?

(02:34)
Things like stress, caffeine, sleep, all these good things. So, I think heart rate is an amazing measure to keep an eye on for recovery rides. It's like the control check and you can do the same. You could use it as a control check for zone two rides, but I think it starts getting a bit complicated for many riders. So in that sense, I take a more practical approach with zone two, I would say you follow the power because it's easy and simple to understand to get it right, focus on trying to just hold a steady power outdoors. That's difficult enough as it is for most people. And once you get doing that, when you compare ride or ride, you can measure the heart rate drift and track the adaptation pretty well. But if you're just doing it on a heart rate, it starts to get very difficult to account for all the other things and see how you're responding.

Cam Nicholls (03:26):

So what do you make of these guys that go out and ride? They do a three or four hour, zone two ride. They're trying to keep themselves in an aerobic state and as soon as they're following power initially, but they're looking at their heart rate, but as soon as their heart rate starts stepping into sort of that zone three, zone four threshold category, they'll reduce the power in order to keep their heart rate down. What do you think about that methodology?

Ben Treble (03:57):

Yeah, I'm not opposed to it. I haven't had a need to over-implement it though myself mostly because it's particularly working with, say when you're working with recreational amateurs, as I said, you got to keep it pretty simple. Sometimes you're just bringing people into the concept of training by power to start with, let alone heart rate on top of that. It's getting a little bit complex pretty quick. That's pretty simple for me. I think it's a good idea. I like the idea of saying, okay, if you are zone two powers 160 watts after two hours and your heart rate should be one 30 and after two hours your heart rate's up to 1 45 at this point, you go, okay, that's a flag. Do we drop the power to try and keep it in the heart rate zone at the same time. It's probably a big question because how do you track your zone two heart rate in the first place? Like all good things, right? You can question zone two, heart rate. Was it based on max heart rate? Is it based on a threshold heart rate? How accurate is that? It's not correlated to the zone two. Heart rate is often not correlated to the zone two power anyway. I know coaches who use heart rate, I know coaches who use power, some use a combo.

Cam Nicholls (05:25):

Yeah, I always, because I see these comments a lot on YouTube, right? Some, I've made a lot of zone two YouTube content in the past and there are a lot of people that tend to, it's almost like the rim versus disc debate. It's heart rate versus power and people seem to get quite fixated on keeping your heart rate within a certain range and not going, I guess ultimately what we're supposedly doing is not getting a big rise out of the lactate system, which keeps you in that aerobic state, which if you were technically really going to monitor, you would need to be taking what a lactate monitor out with you and pricking your skin and taking a blood sample. And when you're going, when you're essentially going down that rabbit hole, it's like who's writing these comments? Who's thinking this way? Is this person seriously trying to make a pro-level team or what are we trying to do?

(06:27)
Because normally we're talking about when we're following power and heart rate for a one hour ride, to me it's just a no brainer. You follow power for a condition rider, two hours, you follow power maybe even three hours. But it's like, okay, there comes a point in time when if you're trying to stay in this aerobic state in inverted commas and you are doing a long ride and you're starting to stress and you're getting your rise out of your lactate system, your heart rate's going up. Once you get to that three or four hour mark, are you better off reducing the power and keeping your heart rate within that specific zone? But how often are you doing that ride? And if you do keep following power, is the adaptation going to be almost as similar as if you followed heart rate and therefore this whole conversation at a recreational and amateur level becomes null and void. You know what I mean?

Ben Treble (07:23):

I've not seen, not saying there isn't, but I haven't seen any specific studies that have tried to compare purely heart rate zone two versus zone two power workouts to see was there a significant difference in the adaptation outcomes. I would say that it's unlikely that you would see anything significant. There'd probably be some individual differences, but that's not necessarily going to be because they were in heart rate or power, but rather other individual genetic differences and whatnot. You brought up a good point though. I mean, yeah, I would use lactate. I have a lactate meter though. I'm a bit of a nerdy scientist. The strips are expensive. I noticed, I think Harry Sweeney on EF Pro, he did an interesting video where he was tracking, he had a big six hour zone two ride, which for most people he was doing more like his zone three really high aerobic work.

(08:28)
And periodically he was yet stopping doing a finger prick and checking his lactate to keep it in a certain range. So he was sort of basing his intensity off power and heart rate together, but then checking it with lactate. And I think pretty soon we'll see continuous lactate monitors come into play. And I think this will really change this question. I mean it won't be a question because it won't be saying, oh, we think the heart rate is a proxy for a shift. In our lactate response, we'll be able to say, is there a shift in the lactate response throughout the ride and change the intensity based on that?

Cam Nicholls (09:14):

And I am assuming sometimes the heart rate's so variable, right? Sometimes it might be and sometimes it may not be as well. It's probably not going to be linear.

Ben Treble (09:23):

You're using it to know when you get out of an aerobic state. But it's like, well, you have to be in a pretty high intensity to get out of, I mean we're always using our aerobic system to some degree at a certain intensity. Fat oxidation completely drops off to zero, but it's a very high intensity to get to that point. And if you're doing zone two heart rate or zone two by power, I don't suspect you're getting close to this intensity where you would be dropping off your aerobic fat oxidation, but your aerobic system is still getting hit, right? We say it comes back to why we do zone two training. Like well, if it's to develop your aerobic capacity, I mean VO2 intervals, which are pretty high intensity, we know as one of the best ways to improve VO2, max, which is our best measure of aerobic capacity. So again, it comes back to some of the other research that pretty quickly says we have to do hard work to get good adaptations, whether that's aerobic or anaerobic.

Cam Nicholls (10:25):

And I've always been like, look, if you can go out and write at 65% of your FTP for three hours, constant pressure, not deviate too much, that's a great ride well done. Don't worry so much about what's going on with your heart rate. Just go do that a few times over the next month or two and that that's a good adaptation. It's a different way of training just doing that versus, oh, but my heart rate's gone up this much, so I'm going to now drop down to 55% of FTP at the two hour mark. And to add another layer to that, and this is just a pure anecdotal experience, I remember when I first got into training, the guy wanted me to have a power meter. I'm talking like 2012, like a long time ago, and I went with heart rate and I started to do these longer three, four hour zone two rides.

(11:18)
And I remember I got to the end of the ride and I could tell that I was really reducing the power through the pedal stroke to keep my heart rate in zone two. So what was I ultimately doing? I was conditioning myself to reduce the power as the ride went on. Whereas when the following year was the event that I was targeting, I actually performed really poorly. And I dunno whether this was correlated, but I did a different coach, different program, but I was training to power. I would focus on my zone two power, and I noticed my heart rate was really drifting a lot during these rides and I was asking him questions, should I follow power? Should I follow the heart? He goes, no, just keep following power. And what you'll notice over time is your heart rate will actually on these longer rides will start coming down and stop drifting less.

(12:05)
You're conditioning yourself to ride at that particular power. So I was like, okay, cool. So I kept doing, over the course of many weeks, months, my heart rate stopped drifting as much and it started producing. I'm like, oh, hang on a sec. I'm now actually riding at a constant zone two power for three hours and my heart rate is no longer drifting into zone three and four. It's actually staying at top end zone two by the end of the ride. And it made me kind of go back to the year prior where I was following heart rate and I'm like, well, hang on a sec. I've conditioned myself in that particular training block to reduce the power as the ride went on to keep my heart rate within zone two. Whereas this year I've just kind of ignored heart rate initially and conditioned myself to produce a certain amount of power over four hours.

(12:54)
And as a result of that, my heart rate's dropped and now I'm operating in zone two anyway. And then I went on and I actually podium in that same event that I was targeting the previous year where I finished 25th I podium. So my training was obviously a lot better and zone two just played a factor into that. But that was a big realization for me that by following power, I was able to condition my body at a zone two level a lot differently. And what appeared to be a lot more effectively with power versus heart rate.

Ben Treble (13:26):

How many races do you go to where the intensity drops off to the end? It usually increases.

Cam Nicholls (13:31):

Exactly. Yeah.

Ben Treble (13:34):

But I mean, we're training a lot of different physiological systems. If you're going to train on zone two on heart rate, it's more focused on training the cardiovascular system. But that's at the same time it's not ignoring, but for simplistic sake, it's kind of ignoring what's happening at the muscular level. And ultimately, whilst the cardiovascular system is vital in the big picture, the energy output and the muscle contraction is what pushes the pedals. So at the end of the day, that's kind of what we care about the most. You need a good cardiovascular system that supports that and underpins that. But training by power is I think, a bit more correlated to focusing on training what's happening at the muscular level. What is the energy output? Well, how much energy does it take to push on what? Race specificity.

Cam Nicholls (14:38):

We're both aligned. I'm glad the science man has the same viewpoint as I do. And that is, yeah, you want to track both, but if you had to pick one, you want to go to go with power. Thanks, Ben, appreciate it.

Ben Treble (14:56):

Great.

Cam Nicholls (14:58):

So if you're looking to do a little bit of zone two training yourself following some power programs, zone two and FTP and more, you can check out RCA has a whole bunch of off the shelf cycling plans. Just go to road cycling academy.com, check out our off the shelf plans and you can start on a training program that will catch you in the next podcast.

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