Rhonda: Got it. So with high-intensity interval training, HIIT, there's... I've heard you talk about, and you've published research, you've written about it in a popular book, the health benefits of high-intensity interval training on VO2max, which I'm sure you're gonna talk all about. But recently, there's been a very...

Another form that's become very popular of training for improving VO2max, which is zone two training, as defined by a lower-intensity sort of lactate threshold training. However, that type of training does require a pretty big time commitment. I mean, anywhere between three to six hours a week. So can someone achieve similar improvements or really good improvements in VO2max from doing, let's say, 20 to 25 minutes of high-intensity interval training three to four times a week? And if so, what... Are we leaving anything on the table if we're not doing that long-duration sort of zone two type of training?

Dr. Gibala: Yeah, so in short, I think you can do more vigorous or high-intensity exercise for shorter periods of time and at least see similar improvements in VO2max. So for the individual who is time-pressed, I don't think there's a need to do three to four hours of what I understand to be zone two training weekly in order to maximize improvements in VO2max.

In fact, there's evidence that would suggest that more vigorous intensity exercise, higher-intensity exercise can potentiate or lead to greater improvements in VO2max or eliminate what's known as non-response. So some people engage in training and it's very frustrating because their VO2max doesn't change at all.

And there's various reasons for that that we didn't talk about. But for example, some evidence has shown that moderate-intensity continuous exercise, even for six months or so, doing guideline-based evidence, roughly 40% of people don't see a measurable improvement in their VO2max. Now some of that non-response was eliminated in a group that was doing the same total amount of exercise but engaging in a more vigorous manner. So that would seem to argue against zone two somewhat, but I think, you know, all roads lead to Rome. You know, there's many different strategies that you can engage in successfully. And I think a big thing is what do you like, right? Do you like and enjoy vigorous intermittent-type exercise? Then maybe it's for you. If you prefer continuous lower-intensity moderate-exercise training and that's just what you like and you absolutely hate intervals, that's okay too.

Rhonda: Can you talk about what VO2max is? We hear a lot about it and why it's important for health, longevity, and maybe why athletes would be interested in it as well.

Dr. Gibala: Sure. So VO2max is the maximum rate of oxygen uptake by the body. It's typically measured during an incremental exercise test. So you get up to very high work rates and that's where you'll see your highest rate of oxygen uptake. It's determined by many physiological factors and processes, but it reflects the peak integrated capacity of the cardiovascular, the respiratory, the blood, the skeletal muscle system to take up and utilize oxygen.

It's clearly important for athletes. It sort of sets the ceiling. You know, and a challenge for athletes in many events is how close to the ceiling can you work for a defined period of time? And so, you know, the higher the oxygen uptake, the better. It's also the clinical correlate of VO2max is cardiorespiratory fitness.

So VO2max is the best objective measure of cardiorespiratory fitness and why fitness is so important. Epidemiological studies show having a higher cardiorespiratory fitness is associated with a reduction in all-cause mortality, dying from all causes, as well as developing many different chronic diseases, cardiovascular disease, type 2 diabetes. So bottom line is having a higher fitness is better. It protects you. It reduces your risk of dying and developing diseases. And the best way to measure that is through a VO2max test.

Rhonda: So you mentioned these epidemiological studies, these observational studies that are looking at the correlation between higher VO2max and, let's say, all-cause mortality. There's a really, I think, important paper that was published in JAMA in 2018 that showed there was an inverse relationship between VO2max and all-cause mortality with no apparent upper limit. And the elite performing athletes or the elite performers had a 80% reduction in all-cause mortality compared to the lowest performers with their VO2max.

So my question for you is, do you think someone who is doing, let's say, you know, again, doing the high-intensity interval training mostly and 20, 25 minutes, three or four times a week, do you think they can be one of those elite? Is that like what you would think would be an elite performer in terms of their VO2max? Or do you have to be an athlete? How can someone... Do we need to do extra, you know, types of training on top of the HIIT to really get to that level, that 80%?

Dr. Gibala: And so there's lots of things there. And I think, to be clear, the way that an individual may choose to engage in physical activity or exercise for their general health is completely different from the way that an elite endurance athlete might train.

And that has to do with lots of things, including what's the total volume of training. So if you're a serious or an elite or very high-level endurance athlete, you're engaged in 15, 20 sessions of training per week. You're training 25, 30 hours a week of training. And the best evidence, you know, gleaned...there's some scientific evidence, largely, you know, opinion from high-level coaches and athletes is about an 80-20 split there is sort of the ideal mix or ratio to optimize endurance performance.

So about 80% low to moderate intensity type training and 20% high intensity training, much of it including interval training. Again, that's the way that an elite athlete might train who's putting in 25, 30 hours a week. I think that ratio can change if we're talking about someone who's engaging in one to two or three to four hours a week of physical activity, and they're looking to optimize how to structure that type of training, fit within their regular lives.

And I think there that ratio can change fairly substantially. And you can incorporate...I would submit that engaging in more vigorous intensity type exercise if you're only doing one, two, three hours a week may potentiate or give you a further boost in fitness. Rhonda: So even potentially one hour, one and a half hours a week, because that's also something...I mean, you mentioned the 80-20 split, and that's something I've heard about a lot, and I think about it because I am not an athlete.

I am, you know, far from an athlete. I am a committed, you know, exerciser, I guess you would call it. I mean, and I am also very interested in longevity and improving my VO2 max. And I wanna talk about measuring that in a minute. So it's, you know, it's not like finding if...you know, is there a minimum effective dose where we can get 80% of the, you know, improvements in VO2 max that an athlete would get?

I mean, that, you know, because if I can get like 80%, you know, I'm in. Like that's a good amount because there's just...there's no way I will be an athlete. Like that's not my life. I can't do that, you know? But I wanna get those improvements in VO2 max.

Dr. Gibala: Correct. No, and, you know, I would consider myself very similar. I'm a committed exerciser. You know, it's in my calendar, I'm sure, much like yours is, and I'm trying to...but, you know, you're busy trying to think what's the best way to structure that. But you know, so a couple of things. I think whatever reason you're active or exercising for, what's the goal? Is it performance?

Is it general health? Is it trying to optimize that time? And I think for a lot of people, it does seem to be, this is how much time I have. You know, maybe it's one hour a week, maybe it's two hours a week. What's the best way that I can utilize that time to promote my overall health? And for those individuals, again, I would submit that there is good evidence that engaging in more vigorous intensity exercise may potentiate the gains. That's not to say it's the prescription for everyone. And the other thing I think we need to remember about VO2 max is the greatest gains are with the smaller changes in fitness, right? So we look at, you know, people who have low, moderate, and high physical activity levels, or low, moderate, and high VO2 max levels, the greatest bang for your buck is just getting out of that low range, right?

And then you continue to gain benefits, but you get diminishing returns. And the extreme would be the elite athlete who's pretty much doing everything right to maximize their physiology, and now they're really just playing on that upper margin. You know, what can I possibly do to eke out a little bit more gain?

That way of thinking and training is not necessarily the way that average everyday people, even serious committed exercisers who are primarily interested in health need to think.

Rhonda: Right. Like Stu, I like Stu's analogy of like squeezing the wet towel and like cutting the last drops out. You know, that's something that, you know, maybe if I was more of an elite athlete that I would be interested in doing.

But right now, I'm like, how can I get to that, you know, where I'm at least 80% of getting that VO2 max? Maybe getting all of it if I could, like going hard and getting it. But you do, going hard, you mentioned intensity, high intensity interval training, 80% max heart rate. There's these, you know, calculators for maximum heart rate.