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Podcast: How high-intensity intervals impact cardiovascular health

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High-intensity interval training (HIIT) — doing short bursts of higher intensity exercise followed by lower intensity exercise for a number of cycles — brings big benefits when it comes to your cardiovascular health.

A HIIT workout increases your peak oxygen consumption (peak VO2), says Dr. Amanda Bonikowske, an exercise physiologist at Mayo Clinic. VO2 is a measurement of the amount of oxygen your heart can pump throughout your body. Increased peak VO2 is associated with a longer life and a healthier heart.

In this podcast, Dr. Bonikowske explains why HIIT is healthy for your heart and how to easily add it to your workouts — or even in one-minute intervals throughout the day.

Dr. Kopecky:

Hello. I’m Stephen L. Kopecky, M.D., preventive cardiologist at Mayo Clinic in Rochester, Minnesota. Great pleasure today to be speaking with Amanda R. Bonikowske, Ph.D., who is the program director for our Cardiac Rehabilitation Program, and assistant professor of medicine here at Mayo. Welcome, Mandy.

Dr. Bonikowske:

Thank you, Dr. Kopecky, for having me today. Pleasure to be here.

Dr. Kopecky:

Yes, well, that’s great. We’re talking about what I think are one of the most exciting, certainly activity topics, which is high-interval intensity training. Could you just give us a brief rundown of what is HIT or HIIT as it’s called?

Dr. Bonikowske:

Yeah. So high-intensity interval training essentially is doing periods of higher intensity exercise and then followed by lower intensity exercise and doing that for, you know, a number of cycles throughout an exercise session.

Dr. Kopecky:

And is there any guidelines for doing it that you tell your patients about. You know, how hard to go, how long to rest in between or, you know, slow down in between the intervals, et cetera.

Dr. Bonikowske:

Yeah, absolutely. The really neat and fun part about high-intensity interval training is that it is infinitely variable. So it can be incorporated in whatever fashion you would like, using whatever exercise modality you would like. You can even use body weight as your exercise modality. So the training is very variable. And then in regards to what I share with timeframe, it can be anywhere from as low as 10-second intervals, which would be more similar to like the Tabata-type protocol, where you’re doing kind of all-out high-intensity for 10 seconds.

But in general, for health and fitness anywhere between 30- to 120-second intervals. And depending on the rest break that you need for that type of interval, you can adjust your work-torest ratios. There are a few protocols. I already mentioned the Tabata protocol. The other fairly famous protocol is the Norwegian or Scandinavian protocol, which is the four by four. Now this protocol is, would be more volume matched to a typical moderate-intensity continuous training exercise session where you’re going to end up with about 30 to 40 minutes of exercise. And that type of, or that protocol does include a higher intensity over a four-minute timeframe, which maybe isn’t always achievable for everyone. But they do a very great job of getting their patients up to that point.

But end of the day it’s whatever is going to be best for your training program. And especially if an individual is brand new to exercise, I would definitely recommend a shorter interval and fewer intervals during your exercise session.

Dr. Kopecky:

Very good. And then how long, you said how much rest they need. How do you know when they’ve had enough rest?

Dr. Bonikowske:

So I would recommend an individual using the rating of perceived exertion scale, by Borg. And so, once they feel like they’ve somewhat recovered, they’re no longer breathing hard and they feel like their reading or perceived exertion is down around 11 or so, then they can, you know, go back to another interval. It’s best to give yourself a longer rest initially and then gauge from there if you feel like you can shorten the rest. And oftentimes as we prescribe interval training programs, we will then change the rest-to-work ratio where we start to reduce the resting ratio.

Dr. Kopecky:

As they get in better shape, they don’t need as much rest.

Dr. Bonikowske:

Correct

Dr. Kopecky:

Go just as hard the next time.

Dr. Bonikowske:

Yep.

Dr. Kopecky:

Gotcha. So what are the advantages of HIIT? I mean, do you get more fit than with moderate-intensity exercise?

Dr. Bonikowske:

Absolutely. The No. 1 advantage is, yes, your peak VO2, our gold standard for how we measure cardiorespiratory fitness. It absolutely is a more potent stimulus for increasing your peak VO2 in a much shorter period of time compared to moderate-intensity continuous training. That’s the number one benefit. And how we can then equate that benefit is that, as we increase our peak VO2, we then see associated reductions in mortality — both all-cause mortality and cardiac-related mortality.

Dr. Kopecky:

Fantastic. And what about getting rid of body fat. Is it better than moderate intensity?

Dr. Bonikowske:

That’s kind of a trick question because nutrition is actually the best approach for getting rid of body fat. Figured you’d like that one. So, you know, the literature is a little bit mixed. What the literature shows in general is that moderate intensity is probably a little bit better at getting rid of body fat per se. However, there are a fair number of interval training studies that have shown reductions in fat-free mass and body composition changes. And I think really the fat-free mass might be the marker, the stronger marker of health, as we move forward and look into the literature more, versus a focus on body fat alone.

Dr. Kopecky:

Does it seem more effective at getting rid of abdominal fat? Every American’s dream.

Dr. Bonikowske:

So I don’t think we can spot train. But I think over time it would be just as effective as moderate-intensity continuous training. So any type of training over a long period of time will definitely work to reduce that fat.

Dr. Kopecky:

Okay, well that really is exciting, this intensity. What, how can you get your patients to incorporate it into their daily activity? Is that possible? Do they have to go to a gym to do this?

Dr. Bonikowske:

So there’s a really neat study and it’s actually a book. His name is Dr. Martin Gibala. And he wrote The One Minute Workout. And so absolutely here at the Mayo Clinic we have steps galore. So what you can do is you can head out to one of the stairwells and you can do 20 seconds of stair climbing three times a day, and do that three times per week. And absolutely, he demonstrated that you still get the same or similar physiologic adaptations as you would to doing typical moderate-intensity continuous training.

Dr. Kopecky:

And that study, he suggested, like, three steps per second. So, a fairly good pace?

Dr. Bonikowske:

A pretty good pace, yes, going up those steps. But some of his other studies also were more low volume. And there’s also an additional study by I believe Chin and colleagues that suggests that even one session of HIIT in a week gets similar adaptations to typical moderate-intensity continuous training, which I think really gets at that — especially for a sedentary individual — anything helps. Any little bit will make a difference and will make an impact. And the literature also shows us that those individuals have the greatest gains, obviously because they have the most to gain. But even that one session of interval training or, even if they don’t do the steps at the exact pace that was done in the study, they’re still going to see significant benefits going from sedentary to even low-to-moderate, moderately active.

Dr. Kopecky:

Hmm. Now, what is the physiology? I mean, you understand this physiology, so talk to us in terms we can understand, but what’s the physiology behind HIIT? Why is that different than moderate intensity to get you in better shape?

Dr. Bonikowske:

You, know, that is a loaded question. But I think part of it is that one, you know, I think the heart is good at doing hard work. So in the short term, it adjusts really well to that type of training. You know, there are studies that show positive remodeling of the heart while we’re doing high-intensity interval training.

But I think also on top of that, individuals are increasing their muscle mass to a greater extent than simply going out for a long, slow durationtype activity. And we see other, you know, vascular remodeling improvements in blood flow. And I think the other big thing is that individuals enjoy it. So there’s a high perception of enjoyment, which is probably greatly related to the time-efficient manner, when individuals pick a shorter duration of exercise. To be done with your exercise session in 20 minutes or less is far more enjoyable for some people, while others, of course, enjoy longer bouts of exercise.

Dr. Kopecky:

Yes, that’s wonderful. It’s so true. So it conquers boredom.

Dr. Bonikowske:

It does, I think.

Dr. Kopecky:

That’s good. What does it do to the lipids? Does it, is it more effective at lowering triglycerides or raising HDL?

Dr. Bonikowske:

So both of those, that’s a great point, yeah. It’s been shown to raise HDL, but then also shown to reduce triglycerides with regular exercise or regular interval training. Now not so much impact on the LDLs. But, that being said, if you do this long enough and you lose body weight, then you will likely lower your LDLs, which is, that’s generally the most potent way to reduce LDLs.

Dr. Kopecky:

Great. What about blood pressure? Is it more effective in vasodilation in causing drops in blood pressure long term?

Dr. Bonikowske:

Yeah. It has also been shown to reduce both systolic and diastolic blood pressure over the short term. Nobody’s really done any long-term randomized controlled trials of resistance training versus moderate-intensity continuous training. So many of the studies have been shorter term. But yes, they do show beneficial effects which relates to some of that vascular remodeling, if you will, that helps to reduce the blood pressure.

Dr. Kopecky:

And when you say short term, what was that, like, six weeks, three months?

Dr. Bonikowske:

That’s probably a good range, yeah, most of them are probably around the sixto 12-week range, which is typical for a physical activity intervention study. But about over that six- to 12-week timeframe, you see those reductions.

Dr. Kopecky:

And is it safe?

Dr. Bonikowske:

It is. So again, it’s infinitely variable, so even in individuals that maybe have some comorbid conditions that we would need to consider or underlying conditions. At this point, the literature has shown that even in say, like, cardiac rehab patients, those that have measured or looked for adverse events, event rates are very low and even at a few of the studies the event rates were lower in the patients’ performing HIIT than the patients’ performing moderate-intensity continuous training. And then, there hasn’t been a ton of literature on more of the low-intensity, low-volume.

But there has been a study by Karstoft and colleagues. It was a low-intensity interval free-living walking program. And within that program I think they really outline something that just about anybody could do. Go outside, go do intervals while you’re walking, and it’s likely going to be safe for just about anyone. Absolutely, the kind of similar contraindications would exist to, you know, if you’re going to do a maximal exercise test or something, there’s some very extreme, like, severe symptomatic aortic stenosis or something along those lines that, you know, it’s probably not safe for. But for the general people, the general population, we’ve seen it done in heart failure and heart transplant in coronary artery disease, metabolic dysregulation, and then of course in healthy individuals. So I think across the board it’s quite safe.

Dr. Kopecky:

Good. Well, Dr. Bonikowske, this has been a wonderful discussion. So you pointed out first that integral high-intensity interval training is better getting you fit. It raises your HDL more, lowers your triglycerides more, vasodilates you, lowers your blood pressure. I mean, it’s something we all need to do a little more of. Dr. Bonikowske, thank you for joining us today. It was great to have you here.

Dr. Bonikowske:

Thank you for having me.

 

Amanda R. Bonikowske, Ph.D.

Dr. Bonikowske is an exercise physiologist at the Mayo Clinic in Rochester, Minnesota.

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