Power vs Heart Rate: How Modern Athletes Train

A common question that we get from a lot of people is whether or not they should follow their heart rate zones or their power zones when they’re doing a workout So I figured this is a good opportunity for us to delve into the pros and cons, kind of a power versus heart rate within the context of structured interval training. So let’s kick things off first though by defining structured interval training so than people know kind of the realm in which we’re talking about this. What are the basics of that Chad. So relative to each person’s own fitness, we get a measure of that Fitness that’s FTP the functional threshold power. So all the workouts are basically scaled to that level of personal fitness and we do interval training which means you work hard for brief periods of time rest and repeat Makes sense, that’s so pretty simple stuff And then let’s get into heart rate kind of a definition behind that it’s it’s kind of basic but heart rate versus power, Nate, do you want to go into that a little bit in terms of what’s being measured with heart rate and what’s being measured with power. Heart rate is it’s just how fast your heart is beating and part of that equation that we don’t have is how much blood is actually coming out so a heart can be really really fast and not put out a lot of blood and that’s called stroke volume or it can beat really hard and pump out less blood and that’s how you see where you have two different people like Chad and I where I have a much higher heart rate than he does even though we’re putting out the same kind of power output. When you’re measuring power you’re actually measuring the actual force output that your body or the power output that your body is doing while its cycling. It’s repeatable, it’s not affected by a whole bunch of things that heart rate is, and you can use that to compare two different people So you mentioned force with power there and that’s the interesting thing with powers it’s measuring not just how hard you’re pressing on the pedals because I think a lot of people might misunderstand that. They see somebody in a really big gear so their legs are turning slowly and they think and that’s a ton of power but that’s not the case it measures not only how hard you’re pressing on the pedals but how quickly you’re spinning them over. Yeah, that’s the definition of power so it’s the it’s the how hard you’re pressing with the rotation. If you’re just pressing really hard and going very slow you’re not putting a lot of power, or if you’re not pressing hard at all and you’re going super fast you’re now putting up a lot power Right, yeah, makes sense. Now one of the problems that we see with heart rate and why we advocate for people just if you have power stick with power in terms of how you’re structuring your work is that it’s subjective, right. And you know we’ve seen this a lot Recently we were up on Mauna Kea, up at really high elevation from sea level all the way up. And that was a great example of elevation affecting heart rate. What are some other things that you guys have seen affect your heart rate? There’s a lot of things: so, just your level of stress, the quality of your sleep, your diet, your level of hydration, caffeine intake, the training stress you know prior to the measurement, your level of recovery, right, a lot of things. The time of day … I actually noticed when I do a block of training with, say one week, at the beginning of that week my heart rate will be higher during the same power output that I do then at the end of the week my heart rate actually goes down more as I get more tired but I can still do those repeatable intervals and it still feels just the same like it doesn’t feel any harder but if I were to train with heart rate I would have … I would not be hitting the prescribe wattage I would be 30-40 watts below Then when I rest up the next week, I’m a little bit stronger, heart rate is really the same each time but I’m seeing my power my power is going up each time Yeah so that’s the interesting thing, and it’s different for each person too Certain people when they might be fatigued they might actually see a different response for a period of time than maybe it’s not a depressed heart rate, maybe it’s actually elevated and it can vary and go back and forth from day to day to a certain extent so it’s really tricky. And I’ve actually seen it different in in different times in my own training where a few years ago, when I would get tired, sometimes it would be higher and it would be really hard to put out that same wattage and I would have a really high heart rate. That’s part of the frustration It’s not that there’s no value in heart rate. It’s now that we have a power meter, like it’s it’s been out for many years now, and there’s great great affordable power meters, and to be able to have that repeatability with every workout — and objectivity — that’s a great way to put it, objectivity, where variables don’t input it. You can still look at those variables and have that advise your training if you want to but it it isn’t the guiding force behind your interval training yeah that’s a good way to put it like if something’s gonna guide it it should be something that you can rely upon and isn’t gonna change from day to day Exactly. Something else that in terms of how heart rates you know the data that you get from heart rate is the fact that it lags compared to power. If you pick up your power output, it’s instantly shown through the power data that you have, but your heart rate, it’s gonna take a while to ramp up. It basically like, if you have blocks for your intervals let’s say you’re working for three minutes, resting for minutes, working for three minutes, then you’re gonna see a very smooth heart rate line through there that doesn’t represent the actual work you were doing. Yeah I think heart rate’s really useful in terms of long term trends when you can take a step back and look at the data over, over you know days and weeks and even months. Same with when you tie heart rate to recovery and that sort of thing. But in the moment, especially when it comes

to short-term interval training, it’s not responsive enough. Yeah, yeah it’s a really tricky thing. In training juniors a lot of the time, they you know, they have heart rate monitors because power meters are really expensive and these kids are working super hard to get their heart rate up to where it needs to be and a lot of the time what ends up happening is, let’s say, we’re trying to get them to do intervals at the pace that they’ll hold during a race. They start out way harder than that should be just because they’re trying to pull that heart rate up to where it needs to be and then thereafter once it gets there they have to really drop that pace down to stay at that point. It’s really problematic and it basically creates a situation that’s that’s pretty unrealistic in terms of actual structured intervals. Yeah and it gets exaggerated the shorter the intervals get too and higher intensity as well which the two typically go hand-in-hand, short intervals high intensity. And Chad, if we’re doing like a 10-minute threshold interval, that’s exactly how like we don’t want to train. If we were training with heart rate, our power output would show that, as we try to hit the target heart rate, I’m gonna go really high with power output and then as the interval went on and as our heart rate raises actually our power output would go down. Yeah and over the course of long intervals like that, especially ones done close to threshold, you would see over over that 10-minute span that your heart rate would start to increase as your power stayed steady. So if you were working by heart rate alone, you would actually start to back off and you drop below the actual power target; the training stimulus might not be exactly what you were shooting for. Yeah, along those lines and I guess we don’t have to get too deep into this right now, but when you mention the training stimulus; when you work at specific intensities, specific adaptations or things happen in your body. And that’s something that’s tricky if you’re using something that isn’t exactly precise. You can get into a spot where you aren’t building exactly what you need to build Now, power on the other hand, it is subjective to one thing with power meters, that it’s an objective metric assuming that you have a good calibration done. Right? That’s correct. If you don’t have your power meter calibrated, and that’s one thing that you can do regularly pretty easily, then you could be dealing with different data. But that would be it. And I want to say one thing. The common term is calibration but the the scientific term is … there’s two parts of it. There’s the calibration and the zeroing. And really in most software, when you click calibrate what it’s really doing is zeroing your power meter. And you can think of that as, when you get on a scale and you push a button and it wants to find out what that level is where there’s there’s no force. So it may take into account like if it’s cranked based, the weight of the pedals. And that’s the zero bit. On calibration it’s something that’s sometimes done at the factory, or done with hanging a weight off it. It’s usually not needed If you’re seeing crazy power numbers with your power meter, I would talk to your manufacturer and find out what the proper way is to calibrate your power meter Yeah, and III agree with talking to the manufacturer. I thought I knew how to do it, and I was doing it just fine. And then I had a problem with my phone and I ended up breaking the power meter. So definitely talk to them on that. That’s something you can do every day. And I’d recommend, I do it before every single ride And it’s not a time, you know, it’s not a painstaking process. It’s really easy It’s database training, so we want to work with good data. Yep absolutely right So, I guess let’s talk about how to use heart rate and how to use power meters You mentioned something like trend analysis, basically. So heart rate variability, resting heart rate, we see it even for like heart rate decoupling Basically this trend analysis that looks at heart rate, and tries to use it to get some insight into either fitness or recovery. And I guess the one thing that you just have to do is you have to keep that big old Salt Lick handy. It’s not a grain of salt but a big old grain of salt handy in the sense that it’s still subjective to the same things that you have that we talked about: illness recovery. Yeah, when we’re talking about heart rate, it’s just that. It’s subjective. It changes from person to person, and within that person it can change from day to day. Yeah, and so within that it’s you know it’s something to just keep in mind that although you may feel that this is like a something that’s really solid it’s still subjective no matter what so kind of keep that grain of salt handy. Post-race analysis I guess is one way? I don’t like to look at my heart rate during the race, because that can be really bad. Yeah let’s get into that. I’ve tried that before I owned a power meter, and I’ve even done it while I’ve raced with a power meter. But if you look at your heart rate while you’re racing, and you have a certain heart rate goal, race day is totally different You are amped up, right? And you probably have a different taper than most your workouts. You might have had more or less caffeine than normal. Everything is different. You’re in a different place, you’re maybe at different elevation… Yeah, you head into it in a wound up psychological state. So your sympathetic system’s already revved up. Your heart rates already elevated past where it usually subsides. Yeah, if you try to hit those same targets, your power is going to be different. And someone might say, well shouldn’t in this wrapped up state, shouldn’t I be aiming for a lower target? But I don’t think the data shows that is that you can actually people do more power in a race even with a higher heart rate and it’s different than in training. So I believe it’s looking, I actually don’t race with a heart rate monitor at all. Or my option is not to display it on my head unit yeah because it gets in my head, and I say my heart rate is, it goes both ways, my heart rates too high right now my

heart rates too low right now yeah and it just and it gets in there, and you get that self-doubt. Or if you look at the power, usually what happens in the beginning of the race you say, well, I’m putting out more power than I should. Let me back that off and pace properly. And at the end you’re saying you’re sayin,g oh I need to try and dig a little bit harder because the power’s too low. Yeah, put yourself in the shoes of one of our juniors at the sea otter classic; a big race that they were really nervous about They had audible alerts set up for their heart rate monitor when they got into their top zone and he was in the top zone and he hadn’t even started the race yet So he was pretty concerned. So that’s a good example of something that if you’re really revved up and really excited, then it’s just elevated that data to the point where it’s not reliable That’s how the body works. I guess that like you said, if you have that heart rate data, post race you can look at it, but once again, and we’re gonna sound like a broken record here but even with that post race even if you’re not looking at it while you’re racing and everything else for post race still keep that grain of salt handy. When you look at that power data, don’t … My point is when heart rate data brings power data into question, then that can get pretty tricky You might be making a mistake in that situation. But power on the other hands pretty easy use. Very easy. Just one number that you’re looking at, and it’s usually least with TrainerRoad, you’re looking at one target wattage that you’re supposed to hit for each interval. Another common question that we get is: let’s say we’re doing five intervals of ten minutes in length of each and your heart rate will drift up after each interval And someone will say, I’m outside of my heart rate zones even though we don’t prescribe heart rate zones we prescribe power zones, but maybe they’ve trained in the past with heart rate zones, and they think on this last interval should I be lowering my power because now heart rates getting too high? No, exactly, energy conversion gets a little more expensive as we fatigue. So over the course of an interval we’ve become a little more inefficient. And and as we become more inefficient our bodies have to work harder to generate the same amount of output. So that heart rate, like I said, trends upward, and again, if we were training by heart rate we’d start backing off and missing the point of the interval. And you’re probably missing a potential point of fitness gain, right? Potentially, sure. The last intervals I find are like the things — depending on, depending on how much you back off, yeah you could completely miss the point Another way that you can use power really effectively is in pacing an effort. And while this might be a little bit more difficult in a variable race; something like a cyclocross race or short track mountain bike, something like that. In a scenario with time trialling or triathlon, it’s super I would say easy to use. Super useful. Yeah, not easy to put out the power perhaps, but easy to use in the sense that it’s a great way to govern your effort, right? Yeah, if you’re a triathlete and you’re not using a power meter, I would seriously consider getting one. What happens is, once you get out of the water and you start on that bike, and there’s everyone around you, it’s so easy to get caught up in that and put out more power than you should. And if you, let’s say, your plan is to put out 200 watts for a Half Ironman, that first five ten minutes when you’re caught up in that, you might be putting out 240 250 and it might feel really really easy because you’re so excited. Then what happens then is at the back half of the run you pay for that part at the beginning. Sure, it’s like any steady-state race effort where you’re just a little wound up a little excited and you go into it a little too hot and that’s the worst time to overdo it. The common … the biggest advice is don’t go out too fast, don’t go out too fast, do don’t go out too fast for any time trial and a power meter lets you not go out too fast Right, it lets you make sure that you’re actually doing that rather than just relying on maybe the perception of the effort or relying on like we said your heart rates gonna take some time to tick up. And then over time it’s gonna keep creeping up so how do you make sure you’re really pacing it well without that power meter? Yeah, exactly, it reigns you in. So if you were to look at heart rate you would go out too easily. If you were to base it all on perceived exertion you would go out way too hard. But power tells you exactly where you need to be. The majority of world records for time trials are done with a slight negative split. Okay, can you explain that what that means, really? What a negative split means is that the second half is slightly faster than the first half. And I know some people, especially in running races, I’m gonna bank some time and then run it slow at the end. That’s not the fastest way to go. That’s not how your body works and a power meter lets you really make sure that you do that negative split. If you were to rely on heart rate, actually opposite would happen. As you are farther on in your race, your heart rates going higher and higher. And then to keep that same heart rate you’d have to reduce your power output, right? And you could try to do some things where you’d say okay I’m gonna plan on getting my power I’m gonna let my heart rate tick up a little bit. But it’s just not as precise as using a power meter. Yeah, when you’re talking about negative splitting, for example, like 40k time trial. Right, so that’s roughly around an hour effort for a lot of people that are, you know, trained cyclists. So they’re looking at that about an hour, they know roughly what they can maintain for an hour. So when we’re talking about negative splitting we’re not saying you know 20 watt slower in the first half and 20 Watts higher the second. It could be as much as five watts, right? Even less. Even less, right, so that’s when we’re talking about that level of precision the power meter can help with pacing a lot Pretty hard to come by if you’re basing it on heart rate. Yeah, now another way to use this for more variable efforts, at least personally I have, is in looking at

my my average or normalized power and I can use that to kind of know how far out of my limits are. But once again, that’s based off of past knowledge You know stuff that I know from previous races and currently where I’m at in my training. How much I should be able to maintain. An example of this is like a solo breakaway in a race if you’re away by yourself, and you’re looking at that power data, you’ll probably know after spending some time training with the power meter roughly how long you can sustain in their current circumstance. Yeah, what’s realistic and what’s unsustainable. Yep, so it doesn’t just have to be a fully constant time trial, it can be really helpful even in other stuff. Yeah that’s like a time trial within a race, because there’s that initial break that you would do in a road race, don’t look at your power meter then, go as deep as you can. Then once you’ve established that break, you can look at your power meter, and if you’re going 80 watts above your threshold, or even you know 40-20 watts above your threshold and you know you have a 30 minute effort left, it’s not sustainable. That’s when you recognize you’re either not supposed to be part of that break or you’re gonna have to figure into a different role. Maybe the guy who’s taking the short turns, or you’re gonna be the guy who’s sitting in the back for the long turns Yeah it’s a great point and actually let’s let’s just go right with that Let’s say you’re in that scenario and you’re in a solo break, or you’re in a time trial, or you know bike leg in an Ironman race, anything like that Nutrition is something that’s really huge and a power meter makes extremely easy. So it’s measuring work and it gives you that work in terms of watts and kilojoules, right? You can see your exact energy expenditure in terms of what you’re putting through the pedals. So it’s really easy there’s no guesswork I guess when you’re talking about pulling in all of that information about how many calories I’m actually burning. It’s pretty well known that the heart rate data can throw you in a spot where you’re gonna be taking in too many calories. When you’re trying to match your nutrient intake to the amount of work you’re actually doing, it’s very hard to do that based on heart rate. It’s quite simple to do it based on power. And I want to say one thing is that with power the thing that we don’t know for calorie intake is a person’s efficiency. It’s that we’re normally guessing that someone’s in there 23-24 percent efficient. Yeah, they’re 23 or 24 percent efficient, and that’s kind of common across everyone. But it’s the best metric we have, and much better than a heart rate based algorithm for calories. It’s a very narrow range. Yeah, it is. It can be super helpful just to make sure that when you get to the end of that race you aren’t deprived. You have enough energy, you have enough glycogen on board, whatever else you need that you’ve got that in there. And in case of a triathlon when you come off the bike, you’re gonna be able to run well. Yeah, which is really helpful. One thing I want to say is that a power meter almost predicts the future, because you can look at it early in a race and it’s gonna tell you am I gonna feel good later or bad later Because if those numbers are high, it’s gonna tell you I’m gonna feel bad later Yeah, but if they’re hitting their goals, or your you’re right around that, it’s it’s most likely gonna tell you that in the future I’m gonna feel good Yeah and you know a lot of the time I’ll go into a race, and perhaps my mindset isn’t exactly where it needs to be, maybe I crashed early on, or had a mechanical, or I just made some sort of mistake, right? And it’s easy to get down on yourself in that time. And whenever you’re down on yourself, the effort seem to feel harder, right? But a lot of the time what I’ll do is in that situation, even though I don’t feel great, I’ll be looking at that data and I’ll be using it kind of like a sign of hope so to speak. Like, I know I can hold this, and sure I may feel more tired today, or I may feel discouraged or something else, but I’m gonna give it my best shot to stick to these numbers — nothing crazy but to be conservative — and many times I’ve found that the truth lies in the numbers. Rather than in my head. Sure. And it allows me to pull a little bit more from my performance. Perceived effort during a race relative to wattage changes. So you can get in a deep dark hole, and you can look at your power meter and say hey I’m actually not doing so bad. Or you can be really excited at the beginning of a race, and it’s easy, and you’ll look at your power meter you’ll say I need to rain things in. Yeah, it’s common I mean I see that in every workout that I do, right? Like in the beginning of my workout, eh, not too bad, I can do this. And then by the end I guess I was a little over exuberant, right? So it’s a good way of keeping yourself in check with that too. So let’s recap here. In short, power is an objective metric as long as it’s calibrated correctly. And it’s a great tool to use for structuring your interval work. It’s a great tool to use for pacing and also timing nutrition, right? Making sure that you’re on board with that. Now with heart rate, though, it’s its objective in the sense that it does measure how many times your heart’s beating in a minute. But it’s subjective in the sense what it implies in terms of performance is what we’re getting into. So it doesn’t get at exactly what you’re doing on the bike in terms of the work So in terms of heart rate objectivity it is objective in that it’s measuring your heart rate, but it’s very subjective in terms of what that tells us. Yeah, that’s a great point. That’s a good way to put it. So it’s different than heart rate in that perspective. And something that we should … recapping to on this, it’s a lagging indicator of that of that effort. Rather than power being one that’s immediat,e which really helps it. It’s just not as responsive. It takes a little time to react. The body has to kind of wind up its resources It’s not that we’re saying that there

no value in a heart rate training. We’re saying that now modern athletes have the ability to own train and race with a power meter. And when you compare those two together, we believe that training & racing with a power meter will make you faster compared to training & racing with a heart rate monitor. Absolutely. So for more information on training and racing with a power meter people can go to TrainerRoad.com