If you’ve listened to Fast Talk before, you’ve likely heard us mention “cardiac drift” or “decoupling” in several episodes. It’s a favorite topic of Coach Connor’s.
The terms refer to cardiovascular drift, which is a “drifting” in heart rate and stroke volume over time. On the bike, we measure it by looking at a rise in heart rate relative to power. Many causes for CV drift have been theorized, including dehydration, muscle damage, cutaneous blood flow, and mitochondrial efficiency.
We’re very excited to have as our featured guest today Dr. Ed Coyle, the University of Texas exercise physiology researcher who published the definitive articles on cardiovascular drift in the 1990s.
In that research, Coyle, who is also the director of the Human Performance Laboratory at the university, and his colleagues demonstrated that even when hydration is maintained, CV drift can be experienced. This increase in heart rate reduces the time the heart has to fill with blood, and this is the main reason for a drop in stroke volume, or the amount of blood pushed out by the heart with each beat.
In a practical sense, when a person becomes dehydrated during prolonged exercise, they also get hotter and experience a greater increase in heart rate and a lower cardiac output and circulation of blood: CV drift.
The exercise becomes very hard when it should not be hard at all. Competitive cyclists interpret this to mean they are getting a “better workout” because it’s more stressful. It certainly is more stressful, but that type of cardiovascular drift is a negative stress. It does more harm than good.
We’ll dive into all of this and much more today on Fast Talk, as we hear from Dr. Coyle and a host of other incredible guests who share their thoughts on cardiovascular drift.
Now, let’s make you fast!
References
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- Coyle, E. F., & González-Alonso, J. (2001). Cardiovascular Drift During Prolonged Exercise: New Perspectives. Exercise and Sport Sciences Reviews, 29(2), 88–92. Retrieved from https://doi.org/10.1097/00003677-200104000-00009
- Dawson, E. A., Shave, R., George, K., Whyte, G., Ball, D., Gaze, D., & Collinson, P. (2005). Cardiac drift during prolonged exercise with echocardiographic evidence of reduced diastolic function of the heart. European Journal of Applied Physiology, 94(3), 305–309. Retrieved from https://doi.org/10.1007/s00421-005-1318-3
- Dawson, Ellen A., Cable, N. T., Green, D. J., & Thijssen, D. H. J. (2018). Do acute effects of exercise on vascular function predict adaptation to training? European Journal of Applied Physiology, 118(3), 523–530. Retrieved from https://doi.org/10.1007/s00421-017-3724-8
- Dawson, Ellen A., Whyte, G. P., Black, M. A., Jones, H., Hopkins, N., Oxborough, D., … Green, D. J. (2008). Changes in vascular and cardiac function after prolonged strenuous exercise in humans. Journal of Applied Physiology, 105(5), 1562–1568. Retrieved from https://doi.org/10.1152/japplphysiol.90837.2008
- Dreisbach, A. W., Greif, R. L., Lorenzo, B. J., & Reidenberg, M. M. (1993). Lipophilic Beta-Blockers Inhibit Rat Skeletal Muscle Mitochondrial Respiration. Pharmacology, 47(5), 295–299. Retrieved from https://doi.org/10.1159/000139110
- Franke, W. D., Boettger, C. F., & McLean, S. P. (2000). Effects of varying central command and muscle mass on the cardiovascular responses to isometric exercise. Clinical Physiology, 20(5), 380–387. Retrieved from https://doi.org/10.1046/j.1365-2281.2000.00273.x
- Fritzsche, R. G., Switzer, T. W., Hodgkinson, B. J., & Coyle, E. F. (1999). Stroke volume decline during prolonged exercise is influenced by the increase in heart rate. Journal of Applied Physiology, 86(3), 799–805. Retrieved from https://doi.org/10.1152/jappl.1999.86.3.799
- Juhlin–Dannfelt, A. (1982). Metabolic effects of β–adrenoceptor blockade on skeletal muscle at rest and during exercise. Acta Medica Scandinavica, 212(S665), 113–115. Retrieved from https://doi.org/10.1111/j.0954-6820.1982.tb00418.x
- Juhlin‐Dannfelt, A. (1983). β‐adrenoceptor blockade and exercise: effects on endurance and physical training. Acta Medica Scandinavica, 213(S672), 49–54. Retrieved from https://doi.org/10.1111/j.0954-6820.1983.tb01613.x
- Kerhervé, H. A., McLean, S., Birkenhead, K., Parr, D., & Solomon, C. (2017). Influence of exercise duration on cardiorespiratory responses, energy cost and tissue oxygenation within a 6 hour treadmill run. PeerJ, 5, e3694. Retrieved from https://doi.org/10.7717/peerj.3694
- Kontogiannis, C., Kosmopoulos, M., Georgiopoulos, G., Spartalis, M., Paraskevaidis, I., & Chatzidou, S. (2018). Mitochondria in β-adrenergic signaling: emerging therapeutic perspectives in heart failure and ventricular arrhythmias. Journal of Thoracic Disease, 1(1), S4183–S4185. Retrieved from https://doi.org/10.21037/jtd.2018.11.01
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Episode Transcript
Chris Case 00:00
Hey everyone, welcome to Fast Talk; your source for the science of cycling performance. I’m your host Chris Case.
A quick introduction to Dr. Ed Coyle and his research on cardiovascular drift
Chris Case 00:20
If you’ve listened to Fast Talk for a while you’ve likely heard us mention cardiac drift or decoupling in several episodes. It’s a favorite topic of Coach Connor. The terms refer to cardiovascular drift, which is a drifting in heart rate and stroke volume over time. On the bike, we measure it by looking at a rise in heart rate relative to power. Many causes have been theorized, including dehydration, muscle damage, cutaneous blood flow, and mitochondrial efficiency.
Chris Case 00:54
Well, today, we’re very excited to have as our featured guest, Dr. Ed Coyle, the University of Texas exercise physiology researcher who published the definitive articles on cardiovascular drift back in the 1990s. In that research, Coyle, who is also the Director of the Human Performance Laboratory at UT, and his colleagues demonstrated that even when hydration is maintained, CV drift can be experienced. This increase in heart rate reduces the time the heart has to fill with blood. And this is the main reason for a drop in stroke volume, or the amount of blood pushed out by the heart with each beat.
Chris Case 01:35
In a practical sense, when a person becomes dehydrated during prolonged exercise, they also get hotter and experience a greater increase in heart rate and a lower cardiac output and circulation of blood. That’s CV drift. The exercise becomes very hard when it should not be hard at all. Competitive cyclists interpret this to mean they are getting a “better workout” because it’s more stressful. It certainly is more stressful. But that type of cardiovascular stress and drift is a negative stress; it does more harm than good.
Chris Case 02:08
We’ll dive into all of this and much more today on Fast Talk as we hear from Dr. Coyle, and a host of other incredible guests who shared their thoughts on cardiovascular drift.
Chris Case 02:19
Now, let’s make you fast.
Trevor Connor 02:24
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Chris Case 03:18
Welcome everyone to another episode of Fast Talk. This is a big one. Trevor, we’ve talked about cardiac drift. We’ve called it decoupling in the past many times in the past. Now we have Dr. Ed Coyle, from the University of Texas at Austin. He is bigger than Jay Z.
Trevor Connor 03:39
I almost looked this up last night. So Dr. Coyle, just so you know, the first time we had Dr. Seiler on the show we called him the Jay Z of exercise physiology because, I admit, I have a bit of a scientific crush on him and a lot of his research, for lack of a better term. Dr. Seiler went through your your department, Dr. Andy Coggan was one of your students, so I almost looked up last night who is the godfather of hip hop because that’s basically who you are in the exercise physiology world.
Chris Case 04:15
It’s a pleasure to have you on the show. Dr. Coyle, welcome to Fast Talk.
Dr. Ed Coyle 04:19
Thank you, thank you, you all are too kind. I’ve been around for a long time. I think things just happen – Good things happen.
Trevor Connor 04:28
We talked about this right before the show, I used to teach exercise physiology and some of your studies were required reading. If you go through an exercise physiology program, any student in one of those programs is going to encounter studies that you’ve done.
Dr. Ed Coyle 04:45
Well, we like to do studies that have some applicability, both to answer the physiology, and explain why or why not performance or stress during exercises is altered. We’re trying to do both basic science and the application.
Trevor Connor 05:03
Today we’re actually going to talk about one of those studies we’ve talked about. So I’ll admit, and I’m glad you’ve mentioned this, I tend to shorten it and just talk about cardiac drift. But really, it’s cardiovascular drift. And that short name changes the meaning. So we really shouldn’t do that. We should talk about cardiovascular drift. But we’ve discussed that a lot in the show, including with Dr. Seiler because he’s researching the implications of cardiovascular drift on longer rides and metrics to monitor that. But you published two studies in 1999, and 2001, that are a couple of those, almost, required readings. Every study that I read about cardiovascular drift since then, at one point or another, references your two studies. And they really did change a lot of the beliefs about cardiovascular drift.
Defining cardiovascular drift
Trevor Connor 06:01
But before we get to that, let me just hit you with a simple question. Could you define cardiovascular drift?
Dr. Ed Coyle 06:06
Sure. Cardiovascular drift, can be also called cardiovascular instability, is where the system is not stable. It’s constantly changing. Some people don’t like the word drift, because drift sounds too frivolous, like it just happens for no reason. But the term is with this cardiovascular drift. And for the most part, the main characteristic is you have a progressive elevation in heart rate, when you are keeping the exercise intensity the same. So your heart rate is drifting upward. At the same time, your stroke volume is drifting downward; stroke volume being the volume of blood the heart pumps per heartbeat. But typically, that can happen while cardiac output stays the same. That is the amount of blood that’s circulating through your body each minute, is not really hampered. The question becomes a chicken/egg question. Well, what’s causing the reduction in stroke volume? Is it the elevation of the heart rate? Or the other way around? So we’ll get into some discussion of that, I’m sure.
Trevor Connor 07:19
And before your study, it really seemed the popular belief was this idea of cutaneous blood flow. So could you explain that a little bit?
Trevor Connor 07:28
Well, let me take a quick step back for any of our listeners who are unfamiliar with stroke volume. As you said before, stroke volume is the amount of blood that gets pumped per beat. So if you think about it logically, in between each beat, your heart has to refill with blood. So if there’s less blood flowing back to the heart, it’s not going to fill as much in between beats. And so you’re going to see this drop in stroke volume.
Dr. Ed Coyle 07:33
Yes, so the studies of this began, some in the 1940s, but mostly 1960s. It was originally thought that the instability was caused by pooling of blood in the skin veins, the cutaneous veins, and that if you have blood that’s kind of trapped or pooling, it doesn’t flow back to the heart very well. And that’s the reason that you’re having this heart rate drift, and this reduction in stroke volume. But most of the studies were done with people exercising at low intensities, they were still getting warm during exercise, exercise less than 10 minutes to 30 minutes. They are increasing their skin blood flow in that time, 10 to 30 minutes. And so they made the association that it’s the increase in skin blood flow, that causes blood to pool in the skin, that reduces the return of blood to the heart. So that’s the classic theory.
Dr. Ed Coyle 08:58
We look for evidence that blood was pooling in the skin, and there really is not any literature of that happening. When people exercise, normally they raise their temperature pretty quickly, if they’re doing any exercise at normal jogging paces, or running paces, or cycling paces they’ll increase their temperature pretty quickly. Once they’re temperature is at 38 degrees centigrade, further increases in temperature don’t really promote more increase in blood flow. But it’s those longer durations of exercise where you show the big drop in stroke volume and increase in heart rate.
Dr. Ed Coyle 09:48
So the point is that the time that cardiovascular drift happened and was most prominent, the skin blood flow and pooling of blood in the skin didn’t appear to be happening, so we didn’t think that could be the likely cause of it.
The importance of watching heart rate with Kristin Legan
Trevor Connor 10:07
We’re about to discuss how Dr. Coyle use beta blockers to research the role of heart rate and cardiovascular drift. But before we do that, let’s hear from Kristin Legan, who is an elite cross and gravel racer. And now as a coach at Rambler Rising, Kristin describes the importance of watching heart rate because of factors like cardiovascular drift.
Kristen Legan 10:28
When working with athletes, and especially doing long rides, cardiac drift comes into play. When I’m talking to them about their long rides, and what power zones they should be in, we also always have to mention the cardiac drift because, especially as they’re getting later into that ride, they’re changing that physiological system that they’re actually working in. So that’s where I prefer to work with, at least on power and heart rate, on all workouts, but especially on those longer rides, because you have to kind of switch halfway through or at least just keep your eye on the cardiac drifts so that once you kind of hit that point, you need to back down the power, even though you might be dropping down a zone that you think you should be in but your heart rate is actually the better indicator at that point.
Testing cardiovascular drift with beta blockers
Trevor Connor 11:18
So you did a really interesting study in 1999, using beta blockers to test this. Can you tell us a little bit about that?
Dr. Ed Coyle 11:28
Yes, we asked ourselves if it’s not pooling of blood in the skin, what else might be lowering stroke volume? And of course, heart rate can. And as you mentioned, if you increase heart rate, you’re reducing the time the heart has to fill with blood and that by itself might be reducing stroke volume. And that’s exactly what we found.
Dr. Ed Coyle 11:54
We had people exercise for prolonged periods and they normally showed reductions in stroke volume and increases in heart rate, but when we gave them a beta blocker – what that drug does is it lowers heart rate, so rather than having a heart rate of 160, during exercise, they had a heart rate of 140, it lowered it back down to the normal levels – and when we lowered heart rate, we immediantly raised stroke volume back to normal levels, despite the fact that we didn’t change the skin circulation, either skin blood flow or the pooling of blood in the skin.
Dr. Ed Coyle 12:42
So, we proposed it was simply that when you exercise, if you experience elevations in heart rate, that you’ll have a concomitant reduction in stroke volume due to reduced filling time of the heart.
Dr. Ed Coyle 13:03
So we can talk about some of the ranges here; I mentioned that with cardiovascular drift, you can see heart rate elevation on the order of 20 beats a minute. So, it’s something that is going to have big effects on your body. The elevation heart rate can come not just from reducing stroke volume during prolonged exercise, and this is exercise that lasts longer than 45 to 60 minutes, as you get hotter, your heart rate is going to go up. And we think, and we’ve shown, that that will drive down stroke volume. But also as you go more prolonged, as your muscles become fatigued, that will send signals back to your brain and eventually to your heart to cause it to beat harder because of the increased stress. That increase in heart rate, for reasons maybe other than cardiovascular – maybe because your your legs are becoming glycogen depleted and you having to recruit more of your fast twitch muscle fibers to maintain power output and that requires more brain activity, cortical radiation, and so your brain is sending more signals to your cardiovascular system and raising heart rate. So there there are a number of reasons why heart rate can be elevated.
Dr. Ed Coyle 14:38
The one that’s most practical, however, is when you become hot during exercise. If the intensity of exercise is high enough, you can become pretty hot within 15-20 minutes of a very intense race, or training session. And that hyperthermia by itself can raise your heart rate, which might lower stroke volume, whether that affects cardiac output and performance or not, is still a really open question. It hasn’t it hasn’t been studied directly.
Trevor Connor 15:16
Which is a really interesting question. I’m actually looking at this study in the Journal of Sports Science and Medicine from 2008 that kind of indirectly explored this. So the title of this study is “The Role of Active Muscle Mass on Exercise Induced Cardiovascular Drift.” So they had athletes do one leg paddling and two leg paddling to see the effects of muscle mass. And one of the things they saw was that the change in core temperature didn’t seem to correlate with the cardiovascular drift that they were seeing. They were actually seeing your correlated more with the amount of muscle mass that was used in exercise.
Dr. Ed Coyle 16:02
And how long was the exercise?
Trevor Connor 16:04
It was an hour. So again, not incredibly long, but it was an interesting study. I’m still a little confused, I’d say, by the use of one leg versus two legs. So basically, they were trying to maintain the relative intensity in each legs. So basically, if you’re on the bike and you’re measuring power, you’d be putting out significantly less power with one leg, but that leg was still doing about the same amount of work that it was doing when you were two leg pedaling.
Dr. Ed Coyle 16:35
We talked about cardiovascular drift in relation to endurance athletes, and certainly is appropriate to do that. But another group who shows cardiovascular drift are very untrained people. It’s been observed that even if you try and do a regular treadmill stress test on a person who has a VO2max of only 20 milliliters per kilogram per minute, half of what the normal value might be, that it’s very difficult for them to reach a steady state; That is when you exercise them continually when walking at two and a half, three miles an hour, their heart rate just keeps going up and up and up.
Trevor Connor 17:22
So it just never levels off?
Dr. Ed Coyle 17:23
It never levels off until they’re very close to the maximum heart rate. I’m not sure what that is due to, I assume they are so out of condition, that the exercise is such a novel stress for them, that they’re getting feedback from all over their body, from the muscles not being used to it, from the breathing, and those signals to the brain are causing the brain to send signals to the heart saying keep keep increasing heart rate because this isn’t right. It’s probably a good response for them to have in order to be able to maintain the exercise for a little while, at least.
How Jim Miller watches CV drift
Trevor Connor 18:13
Let’s hear from Jim Miller, the head of elite athletics at USA cycling who explains how he watches cardiovascular drift to monitor some aspects of fitness.
Chris Case 18:23
When you’re working with athletes, do you watch for cardiac drift? And if so, do you try to train it?
Jim Miller 18:31
Yes. I think that’s the metabolic efficiency of this endurance plus in zone two. Initially, when you have athletes start doing this type of work, you always see cardiac drift. The beginning of season you always see cardiac drift. As they begin to make adaptations, absorb those workouts, then you see less and less of it. And then when you get into like July they should be able to do that same workout with zero cardiac drift – Minus dehydration. If you see dehydration, then you can put two and two together and say ‘Oh, well they train in Texas, of course, they’re dehydrated.’ That’s the cardiac drift not the inefficiency of the athlete.
Current and potential studies on beta blockers and CV drift
Trevor Connor 19:20
So I wondering if I could throw an idea at you, and I will admit I have been losing sleep about even bringing this up because I’m pretty convinced your response is gonna be a combination of “Well duh, and that’s the dumbest thing I’ve ever heard.” –
Chris Case 19:36
Such confidence, you exude it.
Trevor Connor 19:39
But I’ll admit I’m a bit of a science dork. I was fascinated by your study and really just couldn’t get over this question of what is causing that rise in heart rate. So, part of the reason I lost sleep is because I was digging through studies. Again, it was absolutely fascinating in your study that when you use beta blockers to prevent the rise in heart rate, stroke volume also didn’t go down, so basically it prevented this cardiovascular drift. So I was interested if there were any other effects that beta blockers had on skeletal muscle tissue.
Trevor Connor 20:19
I started digging into the research, obviously, there’s tons and tons of research on beta blockers and heart. It was a little harder to find for skeletal muscles. So I was finding a little bit about how it certainly blocks use of fatty acids as a substrate. So I kind of went right back to my original exercise physiology class, I remembered in McArdle they talked about how mitochondria can be a sympathetic driver of heart rate. So I looked up beta blockers and mitochondria and lo and behold, found this 1993 study “Beta Blockers Inhibit Rat Skeletal Muscle Mitochondrial Respiration,” which I found really interesting. So it basically prevents mitochondria from really ramping up.
Trevor Connor 21:17
I continue to dig into the research and then found this really interesting 2007 study that looked at altered endurance cyclists, so these athletes doing 24 hour races. This wasn’t actually a study on cardiovascular drift, though at one point they did in brackets just put the term “oxygen drift”, which I think they were trying to get at the same thing. But they use muscle biopsies on these athletes to look at the impact of this altered endurance event on mitochondrial efficiency. And what they found was actually the same things that you were talking about, there was a gradual rise in heart rate over time, there seemed to be an increase in oxygen consumption. And what they found was that mitochondrial efficiency declined over the course of the event. So the thought that I had is, could mitochondrial respiration be deriving that rise in the heart rate? Could there be a case of – certainly when you’re looking at a long endurance event like this – because the mitochondria becomes less efficient, you need more and more mitochondrial mass to produce the same amount of aerobic energy. And that is going to drive heart rate to increase slowly.
Dr. Ed Coyle 22:51
Interesting
Trevor Connor 22:52
Okay, you didn’t call me down, that’s a good start.
Dr. Ed Coyle 22:56
It’s interesting that the beta blockers – the muscles have beta receptors and when you’re on a beta blocker, your legs are dead. If you try and exercise intensely, to turn on glycogenolysis at 10 C’s above 80% of your VO2max, you really feel it. I’ve always assumed that feeling was because you’re not raising cardiac output enough, because cardiac output could be compromised the higher exercise intensities went on a beta blocker.
Trevor Connor 23:35
So since you didn’t call that immediately dumb, just a couple other interesting things to throw at you; I noticed in your study and several other studies, they look at that short term cardiovascular drift that you see in the first 10 to 15 minutes of exercise. And I can’t help but notice that similar to the length of time for oxygen defici. As I remember, oxygen deficit, so that that slow rise in heart rate and oxygen consumption at the start of exercise is due to the fact that it takes a while for the mitochondrial machinery to ramp up. So there does seem to be a bit of a correlation there as well.
Dr. Ed Coyle 24:13
Yes, definitely beta blockers are going to delay the time/ it will take longer to reach a steady state equilibrium.
Trevor Connor 24:22
The one other interesting thing they had in that 2007 study was their explanation for the decrease in mitochondrial efficiency was due to increase in oxidative stress. So mitochondrias are particularly susceptible to damage from oxidative stress. And so we actually did an episode a while ago on ROS, or natural antioxidants, and found that one of the big differences between elite athletes and less experienced athletes or sedentary individuals is elite athletes have this amazing natural antioxidant systems. Matter of fact, they did studies on athletes, I think they were racing the Dauphiné, and found that their natural antioxidants were so powerful that you saw a net reduction in oxidative stress over the course of the race. Where when they studied far less experienced cyclist put them through a similar level of stress and you just saw them get overwhelmed by oxidative stress.
Dr. Ed Coyle 25:25
Right, yeah, it’s no doubt the muscle, especially, responds to training in a healthy way, not only increasing mitochondria, but also increasing the reactive oxygen species enzymes to protect the cell.
Trevor Connor 25:44
What’s your feeling on this? Is potentially part of the the mechanism here, the mitochondrial respiration?
Dr. Ed Coyle 25:51
If you’re thinking that the beta blockade increases oxidative stress and is going to raise the stress on the cell that will result in more disturbance of homeostasis, the cell will be able to sense that there’s an energy crisis, if you’re not able to use carbohydrate as well, because it’d be a blockade, and that should signal greater stress to the brain and an elevation at heart rate. The elevation heart rate is limited because of the beta blockade. Its affecting the heart, the pacemaker in the heart. I think what would have to be looked at is you’d have to try and give the beta blocker and keep its effect isolated to the muscle; you get the normal heart rate response and cardiac output response to exercise. That quite possibly could show that the muscle efforts are more affected during beta blockade and activating the cardio respiratory center than the brain and in the heart.
Trevor Connor 26:54
That’s fascinating. I have no idea how you would do that, how you would prevent beta blockers from affecting the heart, but you’re right that would be a incredibly revealing study.
Dr. Ed Coyle 27:05
Yeah, you can infuse into the artery, into the femoral artery, a small amount of beta blocker so that it gets bound to the beta receptors in the muscle, none comes back to the heart. So they had to do large pilot work to get those responses so that you know you’re not affecting heart rate during exercise, but you are blocking the muscle to some extent.
Trevor Connor 27:34
I’m actually surprised nobody’s done that study. I would not have thought of that at all. That would be a really interesting study.
Chris Case 27:42
Maybe we can do it Trevor.
Trevor Connor 27:44
Okay, but we’re injecting in your artery
Chris Case 27:48
No, we’ll get a…Jana, perhaps? You haven’t been paying attention, we’ll just use her. Head Coach Ryan Kohler, maybe he’s our guinea pig.
Trevor Connor 28:01
He’s not here. Yeah. So let’s bring him in.
Chris Case 28:04
We’ll volunteer him.
Trevor Connor 28:05
Ryan, come downstairs, we got this little thing we want to do with you. It’s not gonna hurt that much.
Chris Case 28:10
Also, we’re going to do 17 muscle biopsies tomorrow.
Trevor Connor 28:16
So there’s a question for you that I have to ask. How many muscle biopsies have you done on yourself?
Dr. Ed Coyle 28:21
Well, I did only one on myself, you know me doing it. But I’ve had about 12 maybe 15.
Trevor Connor 28:29
I figured. This is the nature of good scientists. They always have to make themselves guinea pigs.
Chris Case 28:35
Exactly. You got tp involve yourself in the science, get deep.
Dr. Ed Coyle 28:39
I realized doing a biopsy on yourself is not that easy. It’s not uncommon and, you know, a lot of times when we’re trying to teach somebody to do a biopsy, it’s easier just to do it ourselves.
Chris Case 28:54
Give me that. I’ll show you how it’s done.
Chris Case 28:59
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Dehydration and cardiovascular drift
Chris Case 29:40
So one thing we haven’t actually talked about but that does come up in discussion of CV drift is dehydration and how that plays a role. So Dr. Coyle I will turn that question over to you.
Dr. Ed Coyle 29:52
During prolonged exercise, longer than one hour, usually two to four hours – as many cyclists routinely do in their training and racin – you will become dehydrated. People are sweating over one to two liters per hour. When you’re becoming dehydrated, you also become hot during exercise, it raises your core temperature. And so that’s an increased stress and that certainly will raise heart rate and lower stroke volume. Also, during prolonged exercise with dehydration, you’re reducing your blood volume and that’ll be a big factor in lowering your stroke volume. Your increasing your heart rate. Those are the the big effects of dehydration.
Dr. Ed Coyle 30:50
The main thing is that you see reductions in cardiac output. Normally, with cardiovascular drift, you have an equal decrease in stroke volume and increase in heart rate so cardiac output stays the same, that amount of blood flowing through the body. But when you become dehydrated, and hypothermic, there’s a drop in cardiac output. That is, there’s a big drop in stroke volume about 25 to 30%. And your heart rate will increase; it may go from where it should be at 145 during the ride up to 170 – not too far from your maximal heart rate. That increase in heart rate, although it’s large, it’s not enough to compensate for the decrease in stroke volume. So the point is, as a result, you have a significant drop in cardiac output, you have a drop in how much blood is flowing through your body to all tissues, muscle has reduced blood flow, skin has reduced blood flow, so that’s why you’re getting hotter because you’re reducing your skin blood flow. And brain blood flow actually goes down a little bit which I believe that Jose Gonzalez Alonso was able to show. Essentially, you are on your way to passing out because blood pressure is also going down. And if you keep it up and keep going, you will eventually of course, have some severe problems with heat illness, and maybe heat stroke, where you’re so hot you’re unable to cool yourself properly.
Dr. Ed Coyle 32:42
The dehydration that causes reductions in skin blood flow, raises body temperature, your heart rate goes up, but it doesn’t go up enough because it’s getting close to maximum. It’s really one of the more dangerous situations during exercise, and it’s something you should try and avoid if possible.
Trevor Connor 33:09
I had a pretty dramatic experience with this. I was at a race called The Cascade Cycling Classic where it’s usually extremely hot, there’s some humidity there, it can have a big impact on you. And I was in the final stage and I remember halfway through I was like a beat below my max heart rate, aven though it wasn’t going fully all out, and noticed I was having a harder and harder time holding a straight line, responding to the field. I almost caused the crash because the field went around a corner and I just couldn’t get around the corner right. And just wen,t I have to get out of here. It’s exactly what you’re describing. I felt like I was starting to pass out and just had to drop out of the field to not cause a giant crash.
Myth:You get a better workout when you’re dehydrated
Dr. Ed Coyle 33:57
Exactly. Yeah, that’s a good description. You know I used to belong to a cycling team, some of who were competitive cyclist, and we’d go out for these three hour rides and I would make sure to have all my water bottles filled and water bottles on the my the back of my jersey and they were out there probably drinking only about a third of what they needed to drink. Sure enough, two hours into the ride they’re struggling on hills that should have been easy for them solely due to just being dehydrated by two to four pounds, a quart and a half or so. They say, “What I get a heart I get a better workout when I’m dehydrated and hypothermic.”
Trevor Connor 34:47
What is the rationale behind that?
Dr. Ed Coyle 34:50
Well the thinking is it’s harder. In other words, when you’re riding with the group, you may not be close to your maximal effort, but if you’re dehydrated and hyperthermic, it’s hard. It gets really hard. And so you’re getting a harder workout. It’s almost like those people who you see running wearing garbage bags or those sweat suits that trap this air essentially so you can’t evaporate and cool. They think they’re getting a better workout – wrestlers are notorious for doing that.
Chris Case 35:28
Yeah, to lose weight, right?
Dr. Ed Coyle 35:30
Yeah, they’re trying to lose weight. It’s just all misguided. And especially with the wrestlers, you’re right, they’re trying to lose weight and they think that if they get hotter and if they work harder, they’ll sweat more and lose weight more quickly. And it’s not true. Your sweating rate is maximal when you’re at just a moderate body temperature of 38 degrees centigrade. But they drive their temperatures up to 40 degrees centigrade. There have been a number of wrestlers who have died because of hypothermia.
Trevor Connor 36:09
Right, they’re just getting that core temperature up to dangerous levels.
Dr. Ed Coyle 36:13
Exactly.
Chris Case 36:14
I’ve even heard of professionals, I won’t mention the specific name, and maybe it’s a myth or a legend about this particular rider, but he would intentionally go out for extremely long rides and bring no water bottles so he wouldn’t be able to hydrate. The thinking being, that harder is better mentality, but also, if I do this in training, but then I’m fully hydrated during the race, my body will do even more with what it has at the time. Sort of building up a tolerance to dehydration, I think might be the rationale there. Of course, again, misguided,
Dr. Ed Coyle 36:54
Definitely, in runners, too. Back in the 60s, marathoners didn’t drink much water; their philosophy on drinking during the marathon was that drink only if you have to, somewhere toward the end, and drink as little as possible. And Jim Peters was running in the Vancouver marathon in 1964, I think it was, and he passed out just shy the finish line. And he was interviewed after he got out of the hospital from hypothermia and almost died and he was asked why he would that happen. Why he didn’t stop and why he didn’t drink more water. And his response was “I was fit. I was very fit, and I wanted to show it.” So it’s it had been a kind of a badge of courage that you can go through a marathon without drinking very much. Fortunately, we’ve left that era behind. Studying cardiovascular drift has been a way to demonstrate how stressed the body is when you’re dehydrated and how dangerous getting hot is. The danger with getting hot is you cook your organs. You get so hot inside that you begin to dissolve some of the membranes of organs. Of course, that’s not a good thing.
Chris Case 38:24
That sounds like something straight out of a horror movie: dissolving your membrane from the inside out.
Trevor Connor 38:30
There’s been a number of studies showing, I think it was 40.5 degrees Celsius, but once your core temperature goes up above a certain temperature athletes just shut down.
Dr. Ed Coyle 38:41
Yes, definitely. And your intenstines are particularly sensitive to that. I forget the name and date of the the Ironman triathlete from Australia who after one race had intestinal problems and it turns out he had to have a large section of his intestines removed because they were essentially cooked during the race.
Chris Case 39:14
Wow.
Trevor Connor 39:15
Okay. I thought I gave a bad image with my race, you just convinced me to make sure I hydrate.
Dr. Ed Coyle 39:25
When you experience the dehydration and hyperthermia, not to the point of passing out, but you feel pretty stressed the next day too. It takes a while to recover from a workout or race like that. It’s just remarkable how when you stay hydrated and you stay cool how much easier it is. In our lab, we typically do th`e heat studies of two hours duration and when somebody becomes dehydrated going at 65% of Vo2max for two hours, it’s a performance test, just to finish the last the last 10 minutes when they’re dehydrated by four to six pounds of body weight. But when we give them the fluids, at two hours, they’re fine. And if we keep feeding them water and sugar, they can get to four hours and show little cardiovascular drift, little muscle fatigue – within four hours, they becoming glycogen depleted so then you have another cause of fatigue popping up, but two hours versus four hours is the difference in performance time.
Long-term repercussions of continuously not hydrating during exercise
Chris Case 40:45
Are there long term repercussions of always doing a poor job of hydrating on rides? I’m looking at –
Trevor Connor 40:55
Chris is staring at me right now.
Chris Case 40:57
Well, I’m as guilty as you are Trevor. I honestly feel like over time I’ve maybe become lazier. Or, maybe I’m just adapted in some way to need less – and maybe that’s a stupid or naive way of thinking, but I feel like every time I go on a ride, I drink less than what is recommended, or is best. So I’m wondering if can you adapt? Can you get better? And B) Are there long term repercussions, long term impacts of being dehydrated every time you exercise?
Dr. Ed Coyle 41:39
Take funner’s, you’ll go out for an hour on, lose about two or three pounds of body weight about a quart of sweat, that’s how they work out. I don’t know of any evidence that small amount of dehydration is harmful, comprises their adaptations. It boils down to this: when you’re training, and when you have your hard days of training – and only maybe three days a week should be your real hard days, go on and off – if you’re a little dehydrated, you may not be able to do those five times five minute intervals. So you’re not going to adapt as much. What I’m saying is if your training is not really well developed, or intense, then it doesn’t matter what you do. It doesn’t matter that much that you’re not drinking a quart of water. That amount of dehydration, even over one hour, we’ve shown that it will affect performance by about 6% in cyclists.
Chris Case 42:50
To get the most out of a really intense workout, you need to have your body in a very well prepared state in order to reap the benefits.
Trevor Connor 42:58
Being properly hydrated.
Dr. Ed Coyle 43:00
Right. If it’s not a really hard ride, then it probably doesn’t matter very much.
Cardiovascular drift and training
Chris Case 43:05
Let’s talk a little bit more about the practical side of things here. Trevor, why don’t you start us off with a bit of an overview on some of the concepts?
Trevor Connor 43:16
Well, first of all, let me take a step back and just say we’re now going to talk about cardiovascular drift and training. And really, as cyclists, what we’re referring to is if you’re riding at that set wattage, you see that rise in heart rate, but we’re not directly measuring cardiovascular drift becasue we don’t have a device on your bike that can measure your stroke volume. So this is why, I’m assuming you’d agree, that this is a correlate not an actual measure of cardiovascular drift.
Dr. Ed Coyle 43:48
Right.
How Cameron Cogburn trained cardiovascular drift
Trevor Connor 43:51
Former pro Cameron Cogburn describes the workout he used to do: aerobic threshold rides that would help him to determine his race readiness based off his cardiovascular drift numbers. But he also explains why, as he became a better cyclist, he started to do this workout less.
Cameron Cogburn 44:08
When I first started riding I used to look at cardiac drift a lot. One of my favorite base building workouts was to go out and ride 2, 3, 4 hours at that aerobic threshold and see if my cardiac drift was under 5%. When I could do a ride of a certain duration at that intensity and have a cardiac drift under 5%, I knew I was ready to race if needed over that time period.
Cameron Cogburn 44:32
As I got more fit, however, the power I found I could do five to six hours was just under 300 watts and I’d only have a cardiac drift of 2 or 3%, so minimal. At least at my hold racing weight of 68 kilos or 72 in kind of that offseason base building part of the season, that’s a huge amount of mechanical stress. I mean a jewels a jewel. And also digestive stress. So I started to maybe do them one or two times a year just to cap off a base building period, but otherwise didn’t really do them anymore.
Cameron Cogburn 45:10
And in my opinion, this is just based on anecdotes, I think the reason you don’t see a lot of very fit pros doing these rides is because they’re indeed massive efforts at their fitness level. And they might be able to handle the oxidative stress just fine, but those other stresses that don’t scale with endurance fitness, I think overwhelm the benefit of doing those types of rides all the time, like on a routine basis. Personally, I’d say in the long run, it’s better to do three days in a row of five hour rides at 260 watts, then one massive six hour ride at almost 300 watts even if you have minimal cardiac drift in the ladder.
Trevor Connor 45:55
We had a conversation with Dr. Seiler, bringing up some of his research, and he’s really been looking into this longer term slow rise in heart rate that you see relative to power as potentially a benchmark of an athlete’s level, of their fitness level. And going back to why I brought up that mitochondrial efficiency, because if you’re seeing a drop in mitochondrial efficiency over time, that’s certainly an indication that you don’t have as good an endurance as somebody who’s able to withstand that oxidative stress.
Is heart rate relative to power a good metric for determining fitness?
Trevor Connor 46:33
So Dr. Coyle we’ll throw it to you: what is your feeling? Is this correlate, this rise in heart rate relative to power, a good metric in training? Or is it just interesting, but it really doesn’t show much about your fitness?
Dr. Ed Coyle 46:49
The extent of the cardiovascular drift is best gained by measuring the increase in heart rate. And the increase in heart rate at a given power, if you’re not becoming hypothermic or too dehydrated – which really doesn’t happen until you’ve been exercising longer than an hour or so – if you’re able to keep your level of hydration and as long as you’re not exercising in a very hot environment where even though you’re hydrated, your body temperature is going up because that by itself will be raising heart rate and lowering stroke volume – there haven’t been many studies on how much heart rate drift there is after that point, going two, three, four hours. We’ve done studies where we train cyclists for four hours, and we do muscle biopsies to see what their glycogen levels are, and that’s why I said before, I think, although we haven’t published it, that when your collection levels become pretty low, and you have to start recruiting more of your fast muscle fibers, that that’s going to raise heart rate just because you need more brain drive, more simple drive, to keep the recruitment level going. As far as using cardiovascular drift, as a measure of fitness, I haven’t seen any data on that.
Trevor Connor 48:25
So hopefully this is just breaking new ground.
Dr. Ed Coyle 48:28
Well, there’s so many things; cardiovascular drift can be caused by reductions in blood volume, increases in dehydration of the blood, increases in body temperature, fatigue of certain muscle fibers and having to recruit more – It’s not such an easy thing to study. The body’s, of course, amazing in its redundancy. So you take away one thing as either a positive or negative and something else steps in and takes over – maybe not entirely but for some part of it. The results are always dependent upon who are you studying: what’s their background or level of conditioning or age? When are you making your measurements? So a lot of what may seem like small details are important for being able to not only understand the science, but for being able to apply this.
Tim Cusick’s view on monitoring cardiovascular drift and training software
Trevor Connor 49:38
We talked with Tim Cusick, coach and Training Peaks WKO product leader, about monitoring cardiovascular drift and training software. Tim fields there’s a value, but talked with us about all the nuances of monitoring it that make it a much harder metric to use than we would have thought.
Tim Cusick 49:56
Again, you go back to the stress strain relationship, right? You need both. Power and heart rate can work together, sometimes they can’t, sometimes they can. Low intensity stamina, that type of low intensity impact measurement, is a place they actually can because they tend to be – when you think about what we’re creating workouts and stuff like that – they’re steady state in general, let’s just call it.
Tim Cusick 50:20
So cardiac drift is important and I do think it’s a indicator of stamina and some aerobic fitness. I don’t want to say aerobic capacity quite, but maybe. The problem is you need to filter out the noise, particularly at low intensity. So there’s not a high variation.
Tim Cusick 50:40
So inWKO, we do measure cardiac drift. So we have some cardiac drift trucks already. And it’s pretty good because it’ll actually put a simple linear regression, which really is a mathematical term, it’ll give you an actual number of that drift. So you could technically call that a drift score. I’m not sure I would, but you’ll have a number of the slope of that, right? So the reality is, we have that ability to measure cardiac death, we have the ability to put a slope to it, we have the ability to put a regression to it. so we get a number. And we say, ‘Okay, here’s what happens over time.’ The problem is if you look at a workout over time, let’s say a four hour ride, and the person stops three times, your heart rate drops down to 65, because you’re sitting and recovering and whatever, that outlier data will absolutely taint what you’re seeing in draft. So we’ve been doing some work on trying to measure your cardiac response to what you’re calling low intensity stamina, low intensity work, but we need to peel out those outliers first. And that’s a little bit tricky. We haven’t found the right way to do it. We are testing two or three different systems, analytics, that will do it. And I think if we can get it right, it would be some pretty good information on measuring the strain that the system is going under during the stress of low intensity work.
Trevor Connor 52:11
That’s a really good point. And so far my only solution has been, anyone of the athletes I coach can tell you, coffee shop rides are not allowed.
Tim Cusick 52:19
Yeah, right. And that’s the key. I do it to mine, too. The number of times I get in an argument with people who are like, “Well, I rode four hours at 108 watts.” I’m like, ‘No, you didn’t. Turn that stupid auto pause off and let’s see what you really got because you had two stops at 20 minutes. Of course, it should be a little higher.’
Tim Cusick 52:37
That is the struggle. We pick up so many outliers. When you’re creating metrics, it’s th hardest thing, right? This is where Goggins is a genius. Because the reason he takes everything down so simple, is to be more specific. There’s so much problems with the data, you get killed. You got to get rid of those outliers. If somebody was going to ride a four hour straight, steady state ride, we can give you a perfect cardiac draft. I could score it, I could show you some really cool analytics on plotting. You could track power at heart rate outputs over time, at low intensity power outputs over time, to look to potentially see improved cardiovascular performance – I don’t want to say fitness again there. So all that’s doable. If the athlete gets rid of the outlier data. It kills that type of high end analytic where you’re using regressions and stuff like that.
Trevor Connor 53:35
I have to give you full kudos and WKO 3; if somebody stops riding for more than a couple minutes, it just condensed it. When I saw a WKO4 and it showed the full length of the time off the bike, I was first like ‘Ugh no I won’t be able to see any of the data.’ But then immediately saw the value because I would see my athletes who would take those super long times off the bike.
Tim Cusick 54:07
I literally have a web recording of me answering the question ‘Why does my mean maximal power not match what Strava says?’ Because Strava buffs out all the stops. So you could stop at nine minutes and 17 minutes for a minute on Strava and it will still count that as a 20 minute peak. And obviously at WKO we never manipulate the data. So people are like but WKO is wrong ,it’s 15 – 20 watts less. No, you stopped. Once you stop it’s not mean maximal power.
Tim Cusick 54:40
We have those metrics and, in that way, we can look at it – and I can create some stuff for you if you guys should come over to me – you also have to define stamina. Tell me what you want, but you have to define stamina. In our definition, stamina is fall off a plateau. So we have a metric called stamina, which is a low intensity metric, but over time, and it basically is the rate of decline past one hour.
Trevor Connor 55:11
My definition of stamina, is ability to maintain homeostasis.
Tim Cusick 55:16
Absolutely. And that’s a great definition. And we took the inverse measurement when it comes to power, because it visually articulates very well, if you have a straight line, which is threshold. And you know, that threshold is somewhere near your one hour power, then you see – so we pick a point of inflection where you begin to drop off. What gets hard in stamina measurement is, and we do it as a percentage score, so let’s say you have an 80% stamina so we’re retaining 80% of your threshold power, but if you only ride your bike for two hours, versus you ride your bike for 10 hours that 80% have dramatically different meanings. And that’s what we’ve not been able to solve in measuring stamina. We can’t take it to any one fixed time period. Now, we thought about making it only if you have a four hour ride or longer or something like that, but then that’s problematic in public software, because everyone complains, why don’t I get a number, and then you have 20,000 tickets in your sport. So you can’t do it, the answer is yes, though.
Is riding at maximal stroke volume a good way to train adaptation?
Trevor Connor 56:25
Let me throw another one at you. I don’t know if you saw there was this recent study in 2018. It was a fairly short study, but they hypothesize that riding at maximal stroke volume is a very important stimulus for adaptation. And then they experimented on cyclists where they had – it was a crossover study, so initially, they had the cyclists just ride steady for 30 minutes, right around vtOne, and show that you saw the rise in heart rate, you saw the decline in stroke volume, and so they actually only really spent about a minute at maximal stroke volume. Then they had them do a series of 3 10-minute intervals. Again, at low intensity right around vtONE, and showed that doing that and taking five minute breaks in between, they tended to stay at max stroke volume longer. So I think it was in the continuous group was about 1.5 minutes at max stroke volume. In the intermittent group, it was about eight minutes at max stroke volume. And so they theorize that that’s a more effective way to train because you’re going to get a better adaptation by averting some of that cardiovascular drift. I don’t know if you’ve seen that or not. But what’s your feeling about that is do you think that’s a good way to train?
Dr. Ed Coyle 57:51
Training for max stroke volume, the best way to do it is with intervals, I believe. But as I understand that study, they were keeping the intensity only at 75%.
Trevor Connor 58:02
Right, so it was low intensity intervals.
Dr. Ed Coyle 58:06
Yeah. So Joe Trinity did a study that was published in the Scandinavian Journal of Physiology. He had trained cyclists to do five minute intervals at various percents of VO2Max all the way up to 100% and an even super maximal over 100%. Stroke volume was pretty constant at 85 to 95% of your VO2max. I think you can maintain a very high stroke volume, even at 95% of you VO2Max for trained athletes. And there been some reports that at that level and at 100% of VO2Max, the stroke volume is even higher at those maximal intensities. I would think that’s the best way to train. That is don’t limit your exercise intensity to 75%. Train more specifically at intensities that elicit VO2Max. There are several studies that have shown that the largest increases in VO2Max in average people at least can be gained if they do intervals at 95 to 100% of VO2Max. They can show amazing 45% increases in VO2Max from a Hickson study in 1987.
Trevor Connor 59:42
Fascinating. So if I’m hearing you correctly, what you’re saying is that the study that I just mentioned the issue is there isn’t that much demand for the muscles for oxygen so the body can afford to let stroke volume drop a bit. When you’re up at VO2Max where your muscles are trying to get every bit of oxygen they can get, your body’s basically gonna say “Yep, Maximize stroke volume.” If you want to spend a lot of time at maximal stroke volume, do hard intervals.
Interval training
Dr. Ed Coyle 1:00:13
Yes. And it’s in line with the specificity of training. And if you want to raise your VO2Max the best training to do that is to do repeat intervals at close to VO2Max. So the most common type of aerobic intervals for competitive runners and probably Andy Coggan – because Andy Coggan did these in my lab for two or three times a week for years – would be exercise for five minutes at VO2Max, the minimum workload that elicits VO2Max, and you can check it because you’ll be getting very close to your maximum heart rate after five minutes, you’ll rest three or four minutes in between and do that five times. Five times times five minutes is 25 minutes of exercise you’d have that at VO2Max. That’s really very effective for raising VO2Max and training the muscles too.
Trevor Connor 1:01:20
We recently had a discussion with another guest about just how painful doing five by five minutes of VO2Max is. But yes, that’s a remarkably effective interval.
Dr. Ed Coyle 1:01:31
Yeah, it helps if you can have a group doing it. We used do it in the lab, we have a bunch of regamasters, so we’d put them in a circle and there’s accountability as a team, there doing it. And certainly you can do this on the road, sspecially when you have a certain hill climb, few people doing it. They are tough, and it is something that I know that I hesitate to do on my own. Or if I had to do them on my own I would try not to make deals with myself and say, ‘Oh, let’s do three today, not five.’
Trevor Connor 1:02:09
Oh let’s make yourself do all five. For some reason, this is a reminder, we had a coach who worked at the Australian National Team on the show a few years ago, and he was telling us about a study they did that they never published. Where are they simulated the Tour de France on trainers. So it was a three week study, having these athletes come in and spend four to six hours per day on the trainers. And his comment was “You should have heard the words they were using to describe me by that third week.” So I’m picturing the same thing, these people hit in a group doing these VO2Max intervals and by the fifth interval, what they’re saying to you and Dr. Coggan for making them do this.
Dr. Ed Coyle 1:02:52
Yeah, I think Coggan didn’t walk by himself. He was before we even got a group together. He’s tough, really tough.
Trevor Connor 1:02:59
I did not know that. That is impressive.
Dr. Ed Coyle 1:03:01
He was doing that kind of training. Of course it wasn’t training outside very much. So he didn’t have much of a tan. And he showed up at the starting line of the state championships, white you know, no farmer’s tan, or cyclists tan for him. People just didn’t know who he was. And he broke away and won the race. Road Race.
Trevor Connor 1:03:25
Oh, wow. Wow, that’s impressive. I did not know this about him.
Dr. Ed Coyle 1:03:30
Oh, he was a national, one of the top two or three in the nation for masters.
Trevor Connor 1:03:35
Is that what got him into researching cycling?
Dr. Ed Coyle 1:03:39
I think so. Yeah. As a junior he focused on the science of cycling.
Dr. Ed Coyle’s introduction to exercise physiology
Trevor Connor 1:03:47
I have to ask what got you into studying exercise physiology.
Dr. Ed Coyle 1:03:50
I was a runner in high school and college and a little bit club after that. Became interested also in the science of running and also went to study with Dave Costal, who is the guru, the father of running exercise physiology and human exercise physiology. I picked up biking after learning some things from the Coggan for the most part.
Trevor Connor 1:04:17
So he convinced me to get on the bike.
Dr. Ed Coyle 1:04:20
Yeah. And a bum knee too.
Coach Sondre Sklari on adjusting intensity to cardiovascular drift
Trevor Connor 1:04:26
Norwegian national team coach Sondre Sklari , knows to reevaluate and possibly adjust intensity when you start to see cardiovascular drift in his athletes.
Sondre Sklari 1:04:37
On the athletes, I coached where if we see a really big cardiac arrest, and it is often that the intensity was too high. Then we have to look at intensity to see if it was higher than normal. And you can of course it could be in warmer climates, if the weather is warmer, then that could probably be the reason. It is something you should take into account and maybe do some adjustments if necessary. Interesting to see when the cardiac drift starts, because if you can delay that part, then you’re probably getting better. So the longer you can wait to get that cardiac drift is a good sign. So I think it’s interesting to follow. As for an indoor cyclists during the wintertime here in Norway, I think it’s a common thing and you can use it to get to know your body and to make some good adjustments and finds for the next workouts.
Take home messages
Chris Case 1:05:42
Well, Dr. Coyle, we always like to close out our episodes with a bit of a take home message. We run around the table, and each take our turn, we’ll start with you this time, what is the most important message people should take from this episode?
Dr. Ed Coyle 1:05:57
When they’re exercising for 30 minutes to an hour, even if they keep the pace the same, the intensity the same, they’ll show a slight increase in heart rate, maybe going from 140 up to 150 – 155. And that’s all normal and fine. If you’re exercising for longer than that, and now you’re going to be losing some body weight becoming dehydrated, you should make more of a plan to take in fluids, water or sport drinks, and try and take them at about the rate that you’re sweating. Usually about one quart per hour works for most people. If you’re going out there for a two hour or three hour bicycle ride, just try and minimize the amount of dehydration you have because that’s the biggest factor in causing it causing you to get hot. And it’s getting hot and dehydrated becomes a real negative stress on the cardiovascular system, and causes large increases in heart rate and reductions in cardiac output. So that’s not good. So try to avoid that situation. And don’t become over hydrated. Don’t drink more than you’re sweating. That is you know, don’t gain weight during a workout or a event. Because if you drink too much fluid, you can become hyponatremic, you drive down the serum sodium levels, blood sodium, and that causes problems with the brain and things like that. So, don’t gain weight during the course of your triathlons. If that’s what you’re doing.
Chris Case 1:07:48
Trevor, what do you what do you have for a closing remark?
Trevor Connor 1:07:51
I think one of the reasons I’ve always been particularly fascinated with cardiovascular drift is it’s one of these things that just shows the remarkable complexity of physiology. As you said earlier, Dr. Coyle, there’s multiple factors that can contribute to this that causes rise in heart rate that you see relative to your power if you’re on a bike. This is why we’ve been saying on the show for a while: don’t just ride at 200 watts and go “Okay, now my body’s responding a certain way.” This is why you need multiple metrics. This is why you need power, why you need heart rate, why you also need to listen to rate of perceived exertion, because our physiology is just so much more interesting and complex than that.
Chris Case 1:08:36
Yeah, I don’t know if I have anything more to add.
Trevor Connor 1:08:40
Great. Well, Dr. Coyle, it’s been an absolute pleasure having you on the show.
Dr. Ed Coyle 1:08:45
Oh, thank you. It’s been fun. And I’m so glad you guys are into the physiology and reading these things. That’s commendable for you.
Trevor Connor 1:08:57
Really appreciate that. Thank you.
Chris Case 1:09:01
That was another episode of Fast Talk. Subscribe Fast Talk wherever you prefer to find your favorite podcasts and be sure to leave us a rating and review. The thoughts and opinions expressed on Fast Talk are those of the individual. As always, we love your feedback. So join the conversation at forums.fasttalklabs.com to discuss each and every episode. Become a member of Fast Talk Laboratories at fasttalklabs.com./join and become a part of our education and coaching community. For Kristen Legen Cameron Cogburn, Sondre Sklari , Jim Miller, Tim Cusick, and Trevor Connor. I’m Chris Case. Thanks for listening
