 Most high-level cyclists primarily care about one metric when they're out riding, and that's power. If they have a heart rate monitor, then the data that they collect with it is usually an afterthought. But not only should heart rate not be ignored, but it may actually be the metric that you should pay the most attention to when you're out on a low-intensity ride. Today's video is a continuation of my discussion with leading endurance sports science researcher, Dr. Steven Seiler. And if you want to check out the first part of this conversation, then I've left that linked in the description and I highly recommend checking it out. Today, the main focus of our conversation is heart rate versus power for low-intensity and high-intensity rides. Seiler gets into more specifics about how exactly to do a low-intensity ride, including how hard is too hard and how long is too long. And then I ask him about heart rate versus power for high-intensity intervals. And spoiler alert, it's not as simple as setting it at your power zone and that's it. There's a lot more nuance in this conversation. So without further ado, let's jump right into it. When we're talking about execution as well, I do want to talk about heart rate versus power, because power is so big with cyclists. Absolutely. Which do you prefer to look at and probably getting a little deeper into this question? On one of these easy rides, should we be pacing off of power or should we be pacing off of heart rate? Because that's a common question that people have about polarized training as well. Yeah, it's a good question and I don't think there is a 100% perfect answer, to be honest. And I'm the guy that's supposed to know a lot of this stuff. But I would start, you got ballpark power outputs. I know when I get on, I mostly train on Zwift. I've got to be honest. I used to be outside a lot, but I'm mostly on Zwift because it's efficient. I know 200 watts for me is below LT1. So I kind of have ballpark. I'm going to be in that 175 to 225 range on most of those easy rides. Because 225, 230, edging into LT, above the LT for me. So that's ballpark. But then duration matters. Because that ride that I'm cruising along at 200 watts and fairly flat, then the first hour, no problem. Second hour, not too bad. Third hour, now heart rate's starting to drift up relative to power. Power's staying the same. Heart rate's starting to slide up. Fourth hour, I'm wanting off the bike because I don't usually do four hour rides on Zwift. And so this is the deal is that at low intensity, you got to think intensity times duration. I generally would start with power because I kind of know through a lot of trial and error and testing, I know where my power is relative to those thresholds. But then I have to remember that that's the external workload. That's the load. But the stress of that workout is not constant. Now I'm introducing and I'm separating two terms. Load, load's neutral. Load is just, now it can be calibrated. It's calibrated against my FTP or my maximum six minute power, whatever you want to calibrate it against, as some kind of an individual calibration. But it's a neutral, it's a neutral construct, if that makes sense. It's just, what's the power output? And now I've got to attach a duration to it. And that changes things because now, you know, even at low intensity cycling, it's not a, you know, this idea of a steady state, it's not a forever steady state. It's a kind of a quasi steady state that we get into. When I mean steady state, I'm saying heart rate staying flat, breathing stable. You know, you feel you can be watching a race or watching a TV show while you're riding. But if you keep going long enough, depending on your fitness, your fiber type, a lot of things, then eventually your brain starts saying, wait a minute, now this is not what it was earlier. Things are getting tougher because of glycogen depletion, because of, you know, reactive oxygen species, lots of things going on, maybe dehydration, if you're not taking care of things. But but now the internal workload is increasing relative to the external. So when you ask me this question, and I have to say, well, I need both. I want that external workload, but but at least regularly, I want to also have my internal workload, so that I can see the how they're changing relative, you know, is internal workload starting to go up relative to the external. And when that starts happening, maybe three hours into it to a long ride for me, now I have to start thinking about, okay, what's my training plan for the week? Okay, if it's an interval session tomorrow, then I'm probably going to stop up at about three hours, because I don't want to go too deep. I don't want to start really stressing my body too much, because then I'm going to start, you know, I'm going to turn on a recovery clock that's going to take longer. And that may interfere with tomorrow's workout. On the other hand, if my plan is to go into that, you know, I want to start, I want to stress my body, I want to stress glycogen depletion, I want to extend, extend, extend, then maybe I do a four hour ride. But now I have to deal with the consequences of that tomorrow. Now I'm using three and four because that's me. Now for a high level performer, that might be five, six, you know, it's going to be calibrated against where, what is your baseline? What is your typical low intensity session? If your typical session is three, three and a half hours, then it may take five to get you really into a situation where you're starting to feel stressed, right? For me, it happens earlier, because number one, I don't ride that long. And number two, I've got a high fast twitch fiber composition. I know that because I've had the biopsy. So I'm not a, I'm not a pure endurance guy. So all of these things factor in. And essentially what you're saying is that if you were to ride for four hours at 200 Watts, an hour at 200 Watts for the first hour is, is not the same stress as an hour 200 Watts in the fourth hour, correct? Beautiful. Yes. And if there's a take home message, at least one of them, that's what I keep trying to get people to understand because unfortunately the metrics that we use, some of them are misleading. Let's just take one. For example, training stress score from training peaks. Hey, training peaks guys do a lot of great work. It's a great tool. I know dear, I know his father, you know, so no, no negatives here. But the training stress score is not a stress score. It's a load score. It's a calibrated load score, which says first hour, second hour, third hour, fourth hour, all the same. Well, that's bullshit. That's wrong. It's physiologically not correct. And so I have to just call and say, no, sorry, that's not that. That is a load score. But I want the stress of that load. And that's different. If I'm hearing you correctly, there's probably a point at which you could stay in your low intensity power zone, but you've been riding for long enough that you're actually starting to stress your autonomic nervous system. And that that would be stressful enough to be considered an intensity rider. Yeah, it may well, it could certainly get there. I mean, let's take a marathon and running a marathon for most people when they start it, it is right around the first threshold, just under right. So it is by definition starting out in kind of the green zone or right at that transition between me under LT one and above LT one, right around there. But then 60% of the way into things, then it starts drifting up. And by the end of it, it's the hardest thing they've ever done. And they need and they need weeks to recover mentally and physically. So, so yeah, you know, you can these quasi steady state efforts over where you're you start on the edge of the threshold and then you drift, you can end up, it can be torturously hard. And then if we start talking about threshold sessions, same deal, except just compresses it even more. Going back to the heart rate versus power question, we haven't gotten to the bottom of which we should be following. But it sounds to me from what you're saying, if the goal is to stay in low intensity, and it's a low intensity ride, we should be looking more at heart rate. Yeah, at some point you need to I think you do need to cross check. That's why when people ask me how to evaluate intensity and monitor, I use this trinity, this three point trinity, which is external power, internal physiology and perception. You can't forget the brain, a well tuned athlete also knows what's going on by just feeling it. Right. And the best athletes, one of the things they do is they listen to their body and they don't ignore those signals. So external power calibrated 200 watts for me, you know, that long strip internal heart rate, maybe lactate occasionally. But then I'm also just listening to my body, you know, my brain is saying, this was like a 10 on the RPE scale when I started, but I'm at about, I don't know, maybe 13, 14 now. That's probably enough today. And so we've been using 200 watts because that's what you ride at a low intensity ride. But for people, for people listening who they all have their own on FTP, their own max heart rate, what percentage of either max heart rate or FTP should they be looking at for these rides to keep it under? Yeah, if you can let me be a little bit geeky, I would say ideally what I'd like people to do is have a little bit more of a thinking, all right, what's my max heart rate during cycling? And what's my resting heart rate? In my case, you know, it's, it's about 166 and 36. I've got a low resting heart rate. I've got a low max heart rate. But what matters here for me is that that difference between the two. So 166 minus 36 is 130. That's what that's how many beats I have to work with. For another athlete that's got 185 and 65 or 188 and 74, whatever. See, these are different combinations. And what ends up happening is your percentage of max heart rate doesn't match up with percentage of VO2. Because of this, you know, there's differences between what's the zero point for different people. For me, it's quite low for others, it's to a third of their max heart rate, it varies. So if I could get people to be a little bit more refined and say, Hey, it's useful to know your resting heart rate, roughly at least, and your max heart rate within a beat or a couple beats. And then you kind of know that percentage of your heart rate reserve. And now I can say, yeah, I'm going to want you at say 60% of your heart rate reserve, something like that, right? Now if we were to do that as a percentage of max heart rate for some people, it might be 65 for some people, it might be 68. Some people might be 70. And for most people, low intensity sessions, these long and extensive workouts, they'll be in that 55 to 65% of VO2 max range. That's where they're at. You know, they're not, people want them to be higher, but they're not. And they don't need to be 60, 65%. And that's where you're using a lot of fat, relatively speaking. You're comfortable, at least in the short term, you can talk. And you know, while you're going, you can, another way of thinking about it is at these intensities, you can, you can be unfocused. I can be looking and noticing the birds and the trees and things going on around me. Whereas once you start going above threshold, your brain starts pushing away at extrinsic information. And it starts zeroing in and you start really listening and you start paying attention to everything that's going on in your body, right? You have, so you've got these two strategies, you've got the distraction strategy and the focus strategy. And it seems like you could almost say there's a threshold for that too. The distraction strategy works when you're at low intensity. But when you start moving into that zone where things are starting to get tough, your brain moves over to a focusing strategy and inwardly focused inwardly directed monitoring strategy where your brain is kind of, is checking constantly how my legs, how's my breathing, right? So that's a way of kind of feeling the difference. Another thing that often is different about a low intensity session versus a higher intensity session that has turned on that sympathetic response is that when you get off the bike and it's been a low intensity session, you'll feel empty and ready to eat. Your appetite is essentially there right away. Whereas if you've been training hard, you've activated the sympathetic nervous system. One of the things that happens is blood flow moves away from the, from the gastrointestinal tract and you're not going to have appetite. It's going to take a while to get it back. And so that is a kind of a poor man's, also a poor man's indicator of saying, have I pushed a bit too hard today? If the goal was to go low, keep it low. You're talking about how you really have to focus when you're doing a high intensity session versus you, there's a lot less focus when you're doing a low intensity session. It's kind of a mentally relieving way to train because I think so many people are in this mindset that whenever they get on the bike, they got to smash it. And that is, that's a, that's a stressful way to train. If that's, if every time you're putting on your kit, you think that you got to smash it, it's actually very relieving to just go out and have a relaxed ride and enjoy the scenery, enjoy being outdoors in my opinion. Absolutely. And I'm telling you, you know, I have, when I talk to some of these really good riders, man, they are there a lot of the times where they are able to cut it up and laugh and just enjoy the ride. They're not hammering every day because they just, they can't, you know, they, they've got to, that's one of the, they have to manage their bodies and understand that, you know, because they're, they're paid to be able to turn it on when they need it. So they can't be going out every day and smashing in a group ride with the team and things, you know. So that, I think this is just kind of, it's very strange. It's almost paradoxical because you would think it would be the opposite, but the, the, the really good athletes, the really high performers with the huge capacity, they seem to be the ones that understand that they can't turn on that engine full blast every day, not even close. You know, it's a resource that they, they hold back and then they use it when they need it. And, and they also understand that the season is long, cycling, there's a lot, even for master's athletes and age groupers and so forth, there's a lot of races that you can choose to do. And so if you're not taking care of your body and managing that energy and managing that recovery and so forth, then you're going to get, you're going to stagnate, you're going to get stale at best and you're going to go downhill at worst. So the elite athletes understand it because that's what they get paid to do, but we can learn from them as age groupers and amateurs because we, we do the same mistakes or we can, we face the same problems. It's just that we're at a lower fitness level, you know what I mean? And we're not training as much, but we still face the same problems. All right. So we've talked about the low, low intensity end of the polarized training spectrum here, but let's go to the high intensity end here. Power versus heart rate for high intensity rides. Do you have a preference there? Here, I would really use a wonderful running coach, Renato Canova. He was here in, in where I live and I've listened to him and we've spoken on Zoom. He's coached some of the, you know, best Kenyon runners in the world and so forth. And he would say, well, early in the season in the early build up, I'm going to be internal load focused, meaning that he's going to have the athletes go on heart rate, go on perception. And that's fuzzy in the sense that if you're feeling, if you're not quite feeling it and you're 20 watts down, it's okay in that build up period. You don't get too locked in on a very specific watt value for your interval session. You're just trying to build and you're accepting, you know, you're trying to hit some heart rate, maybe 90% of heart rate max. But then you may, you're going to get to a point in the season and running if you're, if you're a 10,000 meter runner, you know, at the highest levels, you know what the time you have to be able to perform is, you know, you're going to have to crack 27 minutes. And you know that requires this particular pace. Or if you're a time trialist in cycling, you know that you got to be at 400 watts for, for an hour or whatever. So now you start becoming more external load focused as you approach the competitive season and game day. And so then, you know, and now it's about adding minutes at power, at, at goal power. So it may be three times eight minutes at 400 watts. And then the next week or the two weeks later, you're able to go four times eight minutes. And then maybe you stretch it all the way to five times eight minutes at, at, at goal power. And then you say, okay, now I'm going to slide back. I'm going to up the power a couple of percent and go back to three times eight. Does that make sense? So you use both duration and power, accumulated duration and the specific power. And you use both of them to kind of kind of stair step the progression as you start zeroing in on a goal race or a goal event. Wait, what you just described there, it's almost like a lifter in the gym. Maybe they're, they're squatting at, at 300 pounds. And then when they get to a certain range that they're going to bump up the weight and, and when they bump up the weight, they can do less reps, but they're slowly building up to the point where they can do 10 reps of, you know, I know, 320 and, and then they move on. And the bottom line is to use both intensity and duration in your toolbox also at high intensity. There's a tendency to, to be very focused on intensity. Everybody wants to say they've got a higher, you know, six minute power, five minute power, whatever it might be. And so they're kind of pushing, they're trying to say, I want to go up 10 watts. I want to keep going up, but what, but what's going to be most useful in a race often is going to be that I can do this more repeatedly. I can do several of these bouts in a row, right? That's the way you, you crack the, the field, right? And that's what we see among the best athletes. It's, yeah, their, their peak powers are high, but what they're doing so darn well is they are just keep stretching that rubber band again and again until they, until everyone is off the back. Uh, and that's that repeatability part. It's not what you can do for, for five minutes on fresh legs. It's what you can do for five minutes after four hours of racing. Yeah. You know, or, or the fourth five minute push in the race, you know, that's the one that cracks them. That's the difference. And I think that's useful to think about in training as well is use duration to your advantage, not just in just the power or the intensity. So you've got this, you know, an X and a Y axis and you're trying to expand what you can do in both directions. Thanks for watching. If you want to step up your own training to the next level, then I have online training plans available linked in the description below. If you enjoyed this video, be sure to give it a like, subscribe and share this video with your cycling friends. I'll see you in the next one.