Dr. Rhonda Patrick: For the VO2 max, like measuring the maximal amount of oxygen you're taking in during, I guess, maximal exercise, there's— you mentioned to me most people are very interested in that, and they're not going to get that measured directly. They're not going to a lab like yours or to their, you know, physician doing it. But they want to know, should I do it? Or is there an estimator I can do that's good enough? Or how do I decide if I should or shouldn't? Like what—you know, like athletes, probably, maybe they should. But, you know, so this online calculator, the World Fitness Level you mentioned, maybe you could talk just briefly about the science behind that and how people can decide.

Dr. Martin Gibala: Sure.

Dr. Martin Gibala: So, you know, I'm not associated with this at all, but World Fitness Calculator is— it's a valid calculator for estimating VO2 max. And so what I mean by that is it's based largely on a lot of research that's been conducted in Norway, in particular, Norwegian University of Science and Technology, that they've been real pioneers in a lot of interval training research. And so the bottom line is they have a lot of data on measuring things and seeing how they correlate or are related to or can predict VO2 max. And so of all of the calculators that are out there, I think this is the one that people could trust the most in terms of answering a few questions about their age, their sex, their typical activity levels, and it will give them a reasonable estimate of their VO2 max.

Dr. Martin Gibala: But it's still just an estimate because it's saying you're that typical 40-year-old. It's not going to be able to dial in any better individually, but at least it's going to give you a marker in the sand, a reasonable marker. And even if it's not precisely accurate, you can rest assured that it's gonna allow you to track changes over time. So you plug your answers into the online calculator, it spits out a value and says your VO2 max is 38 or 45. And then you engage in some sort of training program for 3 or 6 months, and then you do it again. And if you see a directional change up or down, hopefully up, you can be reasonably confident that, you know, your training program has been effective at increasing your VO2 max, even if the precise number is not 100% accurate.

Dr. Rhonda Patrick: Yeah, that makes sense.

Dr. Rhonda Patrick: You know, there's a few factors in there that were a little more on the personalized level, like your resting heart rate and your max heart rate and BMI and waist-to-hip ratio and— or waist circumference, I think it was. So, you know, there are definitely some features aside from your age and everything like that, but also the estimation of, like, how intense are you going with your exercise, you know, that's— there's a subjective component to it where I was like, oh, I go hard, you know. So, you know, again, it's kind of good to know that you can use that online calculator. People are interested in probably doing that, but for the average person... Do you think measuring it directly is really—

Dr. Martin Gibala: The other way, as an in-between, is a submaximal exercise test.

Dr. Martin Gibala: And there's a number of validated tests that are out there. We could drop those in the show notes, but where you basically are performing a couple of levels of submaximal exercise, measuring your heart rate, and then essentially plugging it into an equation that's going to extrapolate and say, okay, well, if this is your rate of increase in heart rate, once you get up to your maximum, this is what your VO2 max value would be. Or there's, you know, I don't know if you have these here, but the shuttle run test or a beep test, where basically you're running back and forth between a set measured distance. And after a point, you're not able to keep up. But it's called a shuttle run test or a beep test.

Dr. Martin Gibala: And basically, the more power you're able to exert—or the longer you can keep up as you have to run faster and faster between the two markers—the more closely that result correlates with your VO2 max. So, bottom line is all of these are submaximal exercise tests. They're better than just an online questionnaire, even that validated one that I mentioned, because at least it's providing some data about you. You know, so you can't just say, oh, I'm engaging in vigorous activity. It's going to actually measure your heart rate a little bit. So that would sort of be an in-between. But yeah, the gold standard is having a VO2 max done in an accredited laboratory. And that's going to give you your VO2 max value directly, and it's also going to give you a lot of data on your power outputs, your heart rate, even your lactate, in order to try and look at training zones, for example.