We’ve caused this disruption that our body internally is having to make these changes to and that’s key because they’re the changes that make us fitter and healthier on a day to day basis.

So it’s pretty exciting to realize like, oh, this doesn’t have to take me that long. And in fact, I can expect even better outcomes. Welcome to the Strength Changes Everything podcast, where we introduce you to the information, latest research and tools that will enable you to live a strong, healthy life. On this podcast, we will also answer your questions about strength, health and well -being. I’m Amy Hudson. I own and operate three exercise coach studios.

My co -hosts are Brian Sagan, co -founder and CEO of The Exercise Coach, and Dr. James Fisher, leading researcher in evidence -based strength training. And now for today’s episode. Welcome back to our series on principles of exercise design. If you’ve been with us in this series, we’ve covered various elements of a workout and why those are important for the best results. Today’s episode is all about concentrated cardio. So what we’re going to learn in this episode is what is concentrated cardio?

What does that mean? What does it look like? And what are the benefits of adding a concentrated burst of effort cardiovascularly to a strength training session in order to maximize one’s results. So I’m super excited to delve into this. I think if you are not super familiar with this and how it complements your strength training, this is going to be a great episode for you. So Dr. Fisher, I’m super excited to dive in today.

And I mean, my first question for you is, what is concentrated cardio?

Yeah, it goes by many names. So, in the academic literature, it’s often been called high -intensity interval training, or the other, H -I -I -T. It’s sometimes called sprint interval training. So S -I -T, and it’s even been called a re -hit or reduced energy or reduced exertion, high intensity interval training. So, and they all kind of mean the same thing. Basically, it’s this kind of recognition or this understanding that exercise doesn’t have to be a long kind of drawn out affair that’s you know, a steady state.

It can be short, brief, and intense, which obviously parallels what we talk about with resistance training all the time. But fundamentally, it’s often compared to what’s called moderate intensity continuous training. So the idea of going out for 10, 20, 30, I mean, an hour, two hour, minute run where our body will kind of work hard, but then we’ll plateau or we’ll kind of find a homeostasis during that time. The idea is concentrate cardio. I’m going to group it all into the term concentrate cardio because that’s obviously the brand for the exercise coach. under concentrated cardio, we really disrupt that homeostasis.

So it’s anything that’s akin to that. And it’s really defined by anything or brief intervals of greater than 75 % of maximal power or a near maximal effort interval interspersed with active or passive recovery periods.

Okay, so, so far, you know, what I’m gleaning from this is the difference between steady state cardio and the example you gave and concentrated cardio that we’re talking about today. Steady state cardio, an example would be going on a jog and using the same, maintaining the same level of effort the entire time versus going on a jog and then sprinting and then slowing down again and then sprinting and using a lot of energy quickly. It’s sort of like looping in high effort with modest effort in one session. Is that fair so far?

That’s exactly how it is, yeah.

OK, so let’s go into it a little bit more. So we talked about what this is, you know, bursive effort, higher effort, and modest effort. You know, what are some of the benefits of this? And tell us a little bit more about what this might look like and what’s going on in the body if we participate in something like this.

Yeah, well, the benefits are extensive, and there’s been decades of research around this area. Now, really, we can’t talk about high -intensity interval training without talking about Martin Jabala from McMaster University, who really brought this into the forefront from an academic research perspective. But there have been a number of other academics and researchers who have also looked at this approach to training. And the health benefits. From a cardiorespiratory fitness perspective, our VO2 max goes up, so our ability to take in and use oxygen is improved. which is really our endurance capacity.

So that might be that we can exercise easier at the same intensity or at the same relative intensities or relative speed that might be, or we can exercise for longer or so forth. We also see an improvement in our resting metabolic rate. So that’s the number of calories that we’re burning just at rest day to day. And that obviously links back to sort of our substrate metabolism and our fat use and carbohydrate use as energy substrates for energy production during the day. We see improved body composition. So there’s tons of research that’s shown that high intensity interval training of various durations and various, when I say durations, I mean duration of studies.

Some studies are as short as five days. Some studies are much, much longer. Some of the studies I’ve done, I’ve looked at sort of two or three intervals in a day. Some I’ve looked at as short as two or three intervals in a week. So they’re really not, the idea of this is it’s really not time consuming.

We’ve seen improvements in insulin sensitivity. So people who are pre -diabetic or diabetic improve their insulin sensitivity. and can kind of work towards reversing diabetes. There’s improvements in cognitive function as well. And then from a purely health perspective, we’ve seen you know, reduced risk of cardiovascular disease, reduced risk of breast cancer, metabolic syndrome, obviously linking back to type 2 diabetes, but also long -term Alzheimer’s, which is obviously, you know, now sort of phrased as type 3 diabetes, and even reductions in pain and things like osteoarthritis. So the health benefits are really extensive, and to some extent, mirror what we see from strength training, maybe not as extensive as strength training, but certainly really, really positive.

That’s exactly what I was thinking when you were describing these. I mean, if you caught all these, these are results and outcomes that a lot of people care about. Endurance, body composition, metabolism, cognitive functions, insulin sensitivity if you’re concerned with diabetes. So these are really positive things. And I can’t even imagine, you know, combining with this with strength training, you’re already getting some of this. With strength training, this just must amplify your protective outcomes, I would think, combining this with strength training.

Yeah, absolutely. Absolutely. But the main thing that I think is worth talking about is what people see on a day -to -day basis. So we were obviously talking before the show, and one of the things that we said is day -to -day activities that currently feel hard start to feel easier. So it might be that if you turn and run up a flight of stairs and it’s a flight of 10 stairs, that currently feels really hard or near impossible to do. Well, actually, the idea here is we, to some extent, the analogy is we shift that ceiling.

So instead of us going into the red after running a flight of 10 stairs, running up a flight of 10 stairs becomes easier and easier and progressively easier because we’ve improved our aerobic and our anaerobic capacity. So now running up 20 flights of stairs is as hard as running up 10 flights of stairs previously or running up 30 stairs or so forth. So we’re really moving that ceiling over what our body perceives to be hard work and that’s because we’re pushing our body into the red in a training method. And at the start, we talked a little bit about homeostasis. And we said about when you go for a run and you have that steady state. Well, that’s the key, steady state.

So our body is always trying to find this kind of balance between anabolic and catabolic reactions. You know, as soon as I start exercising, my heart rate will go up so that it can move oxygen around to meet my body’s demands. And as long as my body’s demands then stay in a plateau, so I then keep running at the same pace, then my body will keep working at the same intensity. My heart rate will be elevated, but it will plateau at the point it’s needed at. Well, our body will adapt to that, but it will only adapt so far. Whereas what we do with interval training is we massively disrupt the hermiostasis.

Our body really doesn’t even have a chance to adapt in that 20 or 30 second interval. And that’s the key, the intensity.

Okay, wow.

So that’s pretty interesting. So if you picture, you said a lot there, and I’m picturing like somebody doing an interval on a bike. So you gave a running example. But picture yourself on a bike, and you’re pedaling, and it’s easy. And then you get a burst of effort that you’re asked to give.

You’re saying that you’re massively disrupting your homeostasis during that first interval, where your body barely has a chance to catch up because of the demand that you’re doing. But what’s happening as you participate with this is you are conditioning. If you’ve heard the term conditioning, What I think of when I think of conditioning is you’re getting used to something. You’re conditioning your body to be able to perform any bursts of effort out in the world later. So you gave the example of going up the stairs. If I’m conditioned, going up the stairs is easier for me.

If I’m riding a bike and I do intervals on the bike where I do have to pedal very hard, but I get used to that and conditioned to that, next time I’m on a bike ride and I have a hill, it’s going to feel great. It’s going to feel like I can do this because my body has been conditioned. So just sort of like translating some of the things you just said, I’m super excited to hear it. And I hope that’s a fair synopsis.

Yeah, 100%. That’s exactly right. So if I continue a little bit, so when we talk about disrupting homeostasis, let’s just talk about what some of the research has shown about just to what extent So we can talk about this in two kind of main ways. There’s the metabolic disruption and there’s the oxygen demand. So first of all, metabolically, our intramuscular ATP, so ATP is adenosine triphosphate, that’s energy production and energy use. So our intramuscular ATP can be reduced by about 50 % in just a 30 second sprint.

So that means we take nearly 50 % of the energy out of our muscle in just a 30 second sprint. And that’s huge. That doesn’t happen in any other type of exercise, even in a set of resistance exercises. Maybe through a whole workout, it might, but certainly not through a single set of an exercise. So it doesn’t happen in 30 seconds. And this increased demand for ATP sort of catalyzes a lot of metabolic stress in the muscle, and it causes a rapid depletion of sort of phosphocreatine to kind of regenerate that ATP.

So our glycogen stores to help regenerate that ATP are reduced by 20 to 30%. So we’ve talked a lot about glycogen dump previously, and we’re not going to get into that too much now, but we know there’s a massive reduction in kind of muscle glycogen. And then in that exercise and that regeneration of ATP to kind of restore that deficit, there’s quite a considerable change in the acidity of the muscle. So the metabolic kind of mechanisms mean that the pH level drops quite drastically. So as a product of things like phosphocreatine, And so our skeletal muscle and our blood lactate, and our blood lactate, so our skeletal muscle lactate and our blood lactate increases drastically. And what that really does is it causes our body to be able to produce enzymes to deal with that acidity.

And so those enzymes then are once we’ve been able to produce them once, or once we’ve practiced producing them as a response to this training method, we can do them on, we can produce them on demand when we do normal exercise day to day. So, and hence we get this training effect, which is what you sort of said.

I guess my only question is, you know, during that production of this increased acidity, is that when we feel burn?

Yeah, to some extent that’s, we’ve often talked about that as the burn. It’s not, and it isn’t associated with blood lactate. There’s no real clear answer as to why we feel that burn in the muscles and that pain, that acute discomfort within the muscles. It’s certainly a part of energy production. It’s not likely to be a part of the blood or oscoletal muscle lactate, because it’s You can have high lactate concentrations without the burn, and you can have the burn without high lactate concentrations, but typically they go hand in hand.

So it’s not strictly speaking the burn, but we will almost certainly feel that burn within the muscles. So that’s a tricky question that science just hasn’t answered yet.

Got it. No, that is a fair answer. So no, that’s a really helpful explanation.

Okay. But I appreciate you putting me on the spot there. There are things that I don’t know.

That’s what I’ll always do is I’ll always put you on the spot.

Okay.

So we’ve had that metabolic demand and that’s key, but we now have oxygen demand. And When you exercise to the highest aerobic capacity, to the highest steady state, the highest effort steady state, that’s something called a VO2 max. And it simply means the maximum volume of oxygen that your body can take in and use. Okay. Well, if you do a 30 second sprint on a bike, your oxygen demand far, far exceeds what you can actually take in and use. Hence why it’s anaerobic, it’s not aerobic, it’s not with oxygen.

So you’re creating this oxygen debt or this excess post -exercise oxygen consumption. So after you finish the sprint, you’re probably breathing really hard or panting to try to get air back in. And that’s really key. You know, we can do a re -hit workout or a sprint interval training workout, and our breathing rate could be higher for, it might be higher for up to 30 minutes, purely because we’ve created that massive oxygen debt. Now, we also talked about our intramuscular acidity and our ATP synthesis, and that’s obviously linked to our CO2 levels as well.

So when we have a requirement of oxygen, or our breathing, sorry, is not just about taking oxygen, it’s taking out is taking out CO2. So when we have a requirement of oxygen, we also have a requirement to get rid of that CO2. And so that’s helping lead to that increased ventilation level as well.

And so the blood flow to our active muscles is now around 100 times higher following maximal exercise compared to following traditional exercise or at rest. So what is that going to feel like?

having 100 times the blood flow to your muscles, or why is that good for us? Well, okay. So that’s great for us because the more blood that goes to our muscles, the more we clear out any metabolites. So we clear out any kind of byproducts of energy production, but we also move in all the good things that are in our blood. We move in antioxidants and we move in all the positive things that can stimulate adaptation. We improve capillarization, which is how oxygen actually transfers from our blood into our muscles.

So we have all of these other metabolic processes as well. So really what’s happening is this massive disruption of homeostasis leads to these signaling processes that can impact genetic expression, protein synthesis, you know, and how metabolic improvements, and so forth. So there is just so many good things happening at this stage. Now, it’s not to say that a hundredfold of our blood flow to active muscles is going to feel uncomfortable, or it’s going to feel hard anymore, because obviously we recover relatively quick following concentrated cardio. We’ve caused this disruption that our body internally is having to make these changes to.

And that’s key because they’re the changes that make us fitter and healthier on a day -to -day basis. I mean, there’s so much going on right away. And so are you saying that a lot of this, this disruption of homeostasis is necessary and we’re trying to work at an anabolic level versus an aerobic, right? Or anaerobic, I’m sorry.

Anaerobic level.

Yeah, absolutely. And that’s where the disruption really comes.

Will we not get a lot of these benefits if we stay at the steady state or if we stay simply in an aerobic level? No, we don’t. We simply don’t. When we stay at an aerobic level, we work only as hard as we have to. So we talked previously about muscle fiber recruitment, and our body will always do just the bare minimum to kind of get us through the activity. It’s the lazy student in class that does just enough to pass the test.

But what we’re trying to do is really push that student, we’re trying to push our body into that high effort levels. Well, if you think about working this hard, you just simply can’t work this hard for long. But when you do these short, really brief, high effort intervals, you really put this stress on your body that causes these positive adaptations. And the other key thing that we can say that kind of makes this again, analogous to resistance training is when we’re at that high effort level, we’re recruiting those type two muscle fibers. And there again, the key ones that if you go out for a 20 or a 30 minute run, you’re working aerobically, you’re probably recruiting dominantly type one muscle fibers.

Whereas if you get on a bike and you do sort of five minutes with four or five intervals, like high effort intervals, then you’re recruiting those type 2 muscle fibers as well.

And they’re the ones that we want to adapt, that we want to keep as we age. So you’re saying this really doesn’t have to take long. You said we can’t do this for long. You mentioned a couple intervals.

I mean, how long does one need to participate in something like this in order to achieve these benefits that you just shared? Yeah, so there are some studies that have shown that doing this, the body of research generally looks at sort of three intervals in a week. So generally sort of spaced out through the week, but they can also be put together into the same workout. So it might be a five minute workout that’s got, you know, two to five intervals somewhere within it. The idea is that they can be 20 or 30 seconds of high effort. And The old saying goes, you can either work long or you can work hard, but you can’t do both.

And so the best way to think of it is you’re better working as hard as you can for 20 seconds than working easier for a minute. Cause it’s when you do that real hard work for 20 seconds that you really catalyze those adaptations.

But yeah, it’s really a handful a week. Yeah. The most exciting takeaway listening to you describe all this is basically how many profound benefits we can get in a very short amount of time. And that’s what clients love the most about their workout in the first place is that it’s a short amount of time. but for that time investment, they’re getting so many more benefits, in fact, better, more significant benefits. Even in the cardio example, an hour of cardio, great, steady state, produces a few things.

Concentrated cardio is a lot shorter and it can produce even more profound benefits. So it’s pretty exciting to realize like, oh, this doesn’t have to take me that long.

And in fact, I can expect even better outcomes. Like that’s really exciting. The other thing that’s worth mentioning around this, because a lot of people are sometimes fearful when it comes to, well, can I really work that hard? Maybe I’ve had medical issues. But there’s a lot of research that’s been done looking at high -intensity interval training in people with medical conditions such as diabetes, heart failure, chronic obstructive pulmonary disease, coronary artery disease, and so forth. And it’s really been deemed a safe, effective approach for for multiple medical conditions.

So if you have one of those medical conditions, this is not a reason or that’s not a reason to avoid this modality of training. We would still suggest you seek medical referral from your physician or your general practitioner, but the idea that you’re working hard for 20 or 30 seconds is good and actually can be even better because it’s much more tolerable to work for a short period of time than it is to say get on a bike for 30 minutes if you’ve got a medical condition.

Great. One more question to put you on the spot. Is it necessary to track our changes in heart rate during a concentrated cardio session and why or why not? you can absolutely track your heart rate during a cardio session. What you might see, so there’s a couple things that could happen, and obviously there’s a few things. It could stay the same, it could go down, or it could go up.

So if it goes up, that’s something fine, because as you improve your fitness, what generally happens to our heart rate is if you take somebody that’s got a resting heart rate of, let’s say, 80 beats per minute, and then they’ve got a maximum heart rate of, say, 150 or 160 beats per minute, well, as they get fitter, as they improve their cardiorespiratory fitness, what happens is it broadens, it widens, but it winds up both ends of the spectrum. So their resting heart rate now might come down a little bit. So it might drop by five or 10 beats per minute, but their maximum heart rate might also go up by five or 10 beats per minute. And that’s simply just their capacity to, or their body’s demands at rest and their capacity to exercise at those high levels. So if you’re doing concentrated cardio and you find, actually, I got to an all time high in my heart rate, That’s great.

That shows that you’re working really hard and that’s wonderful. If your heart rate stays the same, then obviously it’s saying that you’re working at hopefully a higher power output, but your heart rate is at the same level. So if you can imagine if you’re pedaling and you’re pedaling at 300 watts today and your heart rate is 150, but tomorrow or next week you’re pedaling at 320 watts and your heart rate’s 150, that’s an improvement because it’s a higher power for the same heart rate. So that’s still a win. And then the final one is your heart rate could of course drop. So if you keep the same power, so if you’re pedaling at 150 beats per minute at 300 watts today, that’s great.

But if next week you’re pedaling at 140 beats per minute at 300 watts, well that’s showing that your body doesn’t have to work as hard to get to that same power output. Now what I would say if that’s the situation is, maybe now you can push your heart rate back up to that 150 and see where your power could get to, but we can’t have a win every day. So we can take small victories from all of these things that we see.

But heart rate is certainly a metric we can look at. Power output might also be a metric we can look at. Or if we’re not interested in tracking it, then just knowing that you’ve worked as hard as you can or worked as hard as you’re willing to do on that day for those intervals, that’s enough. Yeah, you’re going to feel yourself recovering slightly between your intervals. And so that’s the goal. Your goal is for your muscle demand to recover or to drop back down and then go back up.

That is kind of like the whole thing, the whole secret. And so you’re going to feel your body doing that.

And so that’s really where the outcomes are, not in the number that you’re seeing. So thank you for breaking that down, though.

That does help, because I’m sure some people wonder that. The other thing that people might see with their heart rate, as you sort of just said then, but just for me to put some clarity to, is if they’ve got to a heart rate of maybe 150 or 160 beats per minute, it’s how quickly their heart rate comes back down and they recover after the exercise.

Another really good sign of fitness, if your heart rate can come back down after the exercise relatively quick, then that’s showing that you’re really improving your fitness. And why is that? Why is it good that the heart rate drops faster and showing that you’re more fit? Yeah. So what we want is for our heart not to be just at a high heart rate all the time. We want our heart to respond to the stimulus.

So when we’re not doing much, we want it to be low. When we exercise, we want it to jump up. When we stop exercising, we want it to come back down. If it stays high for longer, it shows that we’re in that oxygen debt for longer. So it might stay high because We’ve done, you know, more intervals or we’ve done a longer workout or it’s been a bigger stress on our body.

But ideally we want it to come back down because the demands have stopped because our body is recovering.

So it’s moved the oxygen around the body.

It’s recovered that oxygen debt that we created with the intervals. And now we can kind of get back to our plateau, our steady state. Gotcha. Okay. That makes a lot of sense. This is really cool.

And if you’ve experienced concentrated cardio at a studio, you know the power of it. I still remember when I first started working out at a studio and I ended my workout doing a interval on a bike. I just would sit there afterwards for like ever for an hour because I was so depleted.

I was I wasn’t used to it.

And and I knew it was so, so powerful because I really felt like I had nothing left.

But like you’re saying, that’s sort of what the disruption needed to trigger so many of the changes that I was looking for. And so it’s really a net positive. Awesome. Great. Well, thank you so much for explaining this, Dr. Fisher. And we will see you next week for the final installment in this podcast series, Principles of Exercise Design.

Until then, we hope you remember strength changes everything. Thanks for listening. If you enjoyed today’s episode, please share it with a friend. You can submit a question or connect with the show at strengthchangeseverything . com. Join us next week for another episode and be sure to follow the show on Apple Podcasts, YouTube, or wherever you get your podcasts so that you never miss another episode.

Here’s to you and your best health.