But I want to start by talking about cardiorespiratory fitness, healthspan, and longevity. So VO2 max is a measure of maximal oxygen uptake, which reflects an individual's ability to utilize oxygen during exercise. It's considered one of the best indicators of cardiorespiratory fitness, and it's associated with improved healthspan and increased lifespan. Higher cardiorespiratory fitness levels, as measured by VO2 max, have been consistently linked to reduced risk of mortality and longer lifespan. So in the podcast, when I use the term VO2 max, just keep in mind that it's a measurement of cardiorespiratory fitness. The greatest longevity benefit that comes from improving your VO2 max is from people starting from a below-average VO2 max and moving anywhere above average.

So even going from a below-normal VO2 max for your age group and gender to low-normal is associated with a 2.1-year increase in life expectancy. Bumping that up, going from below-normal to high-normal VO2 max is associated with a 2.9-year increase in life expectancy. Going even further to the upper limit of normal is associated with 4.9 years, so almost a five-year increase in life expectancy. On average, each unit increase in VO2 max, so that's 1 milliliter per kilogram per minute, is associated with a 45-day increase in life expectancy.

In another study involving only men, for every 10-unit increase in VO2 max, so this would be then 10 milliliters per kilogram per minute, there was a 17% lower risk of death from cancer and an 11% lower all-cause mortality, so dying from many different non-accidental causes of death. Another study published in JAMA in 2018 found that there was no apparent upper limit to the benefit of cardiorespiratory fitness on mortality within normal ranges of human life expectancy, of course. In fact, the study reported that elite performers, these are people that performed in the top 2.3% on the fitness test, had an 80% reduction in mortality risk compared to the lowest performers, so they performed in the bottom 25% on the fitness test.

And if you compare the elite performers to the high performers, so these folks did really well but they were just under the elite, they were between the top 25% and the top 2.3%. The elite performers had a 20% mortality risk decline compared to even those high performers. So going back to what I said earlier about just moving out of that low fitness group will give huge advantages on life expectancy. So people in the low fitness group had a five-fold higher risk of death than the elite performers, but what is also so interesting is that the risk of dying due to low fitness was similar or even bigger than risks associated with having heart disease, smoking, or diabetes. So being fitter is really good for your health at every level of fitness, and there's always room for improvement.

So the question is, well, how can we improve our VO2 max? Lots of different training protocols, Zone 2 training, for example, high-intensity interval training, you know, vigorous-intensity exercise, all improve cardiorespiratory fitness and can increase VO2 max. HIIT has been shown to significantly improve VO2 max even with shorter training durations. This is because HIIT recruits both aerobic and anaerobic energy systems and increases the intensity of the workout, resulting in greater cardiovascular stress and then adaptations. But this is important. There are individuals who engage in more moderate-intensity, steady-state Zone 2 training who do not experience significant improvements in VO2 max.

In fact, research has shown that approximately 40% of people do not see a measurable increase in their VO2 max even after engaging in guideline-based moderate-intensity exercise, which is about 2.5 hours of this type of exercise per week for several months. But when these so-called non-responders incorporated more vigorous-intensity exercise, such as high-intensity interval training, they did start to see improvements in VO2 max. So this suggests that adding higher-intensity exercise to an exercise routine can help eliminate that non-response and can lead to greater benefits in cardiorespiratory fitness.

The reason for non-response to moderate-intensity exercise is not completely understood, but the addition of vigorous-intensity exercise is important for overall improvements in VO2 max. And engaging in more vigorous exercise seems to provide a stronger stimulus for physiological adaptations that lead to increased cardiorespiratory fitness. So again, I think these findings really highlight the importance of incorporating vigorous-intensity exercise, particularly maybe high-intensity interval training, into a training routine.

And obviously, for individuals who are time-pressed and can't dedicate several hours per week to doing a more Zone 2 type of training, including shorter sessions of higher-intensity exercise can still have significant improvements in VO2 max and overall health. So you might be wondering, you know, how much time do I dedicate to my more vigorous type of exercise versus a more moderate intensity Zone 2 type of training? And I really think that answer depends on a lot of factors, your individual goals, what you enjoy doing most, what you're going to do the most. I mean, all of those things are important because at the end of the day, establishing a habit, having an exercise routine that you're going to consistently do is what is most important.

For endurance athletes, I mean, the answer is easy, right? You're already dedicating several hours a week to Zone 2 training, and about 20% of that training is dedicated to shorter, higher-intensity workouts, more vigorous-intensity workouts. And this is commonly known as the 80-20 rule. But remember, these are people doing extensive amounts of training, anywhere between 10 and 30 hours a week. I think it's a common misconception to apply that 80-20 rule to any committed or casual exerciser who is doing well under 10 hours a week. So think about someone who is a committed exerciser, maybe you work out three to five days a week. How much of that time should be spent doing vigorous-intensity exercise?

I would say for VO2 max and other adaptations we're going to discuss, including the brain, about half of that exercise-training time should be spent doing vigorous exercise. So, again, you want to be at least 80% of your maximum heart rate or more. Obviously, there's resistance training to incorporate as well into any training program. Casual exercisers, people who work out maybe two to three times a week, should probably spend more than half of their time doing more vigorous-intensity exercise. I think this ensures you're pushing your limits and getting adaptations and fitness gains in a shorter period of time. There are a variety of VO2 max training protocols.

So for people looking for that more vigorous exercise, using high-intensity interval training to improve their VO2 max, the key here is longer intervals. So incorporate longer intervals, such as two, three, four, maybe even five minutes at the highest workload you can sustain for that time, and perform four intervals with rest and recovery between each one. This protocol may require maybe a 20-minute time commitment, but it can lead to significant improvements in VO2 max. There are a few examples of VO2 max training. Dr. Martin Gibala, who was a recent podcast guest, gave a variety of examples of this. There are three- to five-minute repeats at the highest sustainable intensity.

We talked about you doing those three- to five-minute intervals that you can maintain, and then you rest and recover and repeat those intervals for a total of 20 minutes. I think a popular variation of this is called the Norwegian 4x4 Interval Training Protocol. So the intervals are four minutes long, and you're aiming for about 85% to 95% of your max heart rate or the maximum level of intensity you can maintain for the entire four minutes. These intervals can be brutal. So the recovery period is three minutes long, and the intensity is significantly lower, like light exercise, more like a Zone 1 training exercise. You want to allow yourself recovery time, the clearance of lactate.

You want your heart rate to come down significantly so that you can prepare for the next four-minute interval. So these four-minute intervals are repeated four times, and again, in between each interval is a three-minute recovery. So that's the Norwegian 4x4 Interval Training. There's another type of VO2 max training protocol. It's the one-minute on, one-minute off protocol. This is where you perform one minute of intervals at the highest intensity you can do for one minute, and then it's followed by a one-minute recovery period. And then you repeat this interval pattern 10 or maybe five times for about 25 minutes or so. And this protocol also is effective at improving VO2 max, and it does provide a lot of flexibility in terms of time commitment.

It's also not as grueling as doing a four-minute interval. One-minute intervals are a little less intense and less painful. Obviously, these protocols are sort of templates. They vary a lot based on individual fitness and goals. There are other protocols out there that can improve VO2 max. The key is a longer interval, longer than something like a 20-second Tabata interval. So, probably at least one minute at the highest sustainable intensity you can do. I think the Norwegian 4×4 protocol is probably one of the best HIIT protocols out there for improving VO2 max. So how do you measure VO2 max?

Without equipment found in an exercise-physiology lab, it's obviously challenging. There are several tests that have been developed and verified for estimating your VO2 max. They don't directly measure maximum oxygen uptake, but they predict your VO2 max based on the relationship between exercise intensity and oxygen consumption. They're useful in determining whether you're improving VO2 max when testing a training protocol. There are a couple of validated tests in the scientific literature that can be done. Probably one of the best is the 12-minute run or walk test, depending on your level of fitness. It's also referred to as the Cooper test.

And it involves having the participant run or jog as far as possible in 12 minutes. So you're supposed to pace yourself evenly. You don't want to start too fast, and the test should be conducted on a flat surface, so like a track field is the best. You don't want to have hills and stuff because it's about the maximum amount of distance you can cover in 12 minutes. And if you have hills and stuff, that's going to lessen that. It's going to be more challenging, and the distance won't be quite as far. So you'll need a fitness device, something that can record your distance, an Apple Watch or Fitbit or something. And depending on your fitness level, you can walk or you can run or a combination.

So the distance covered within that 12-minute period serves as the primary metric for evaluating VO2 max, which is then estimated using a formula. It's the distance in meters minus 504.9, divided by 44.73. And you can look this formula up. Just look up the Cooper test to find the formulas online. Again, there are some other validated tests, but I think that's probably one of the better ones out there. You'll need a device like an Apple Watch or another device that can measure your distance. Some of these devices and wearables also estimate VO2 max during exercise using heart rate and motion data.

You know, for best results, you have to make sure all your personal information is in there, like your age, weight, gender, and all that stuff. But that's another possibility. I would say the 12-minute run or walk test is a more—it's a better way to do it, particularly if you're trying something like the Norwegian 4×4 HIIT protocol and want to measure VO2 max improvements. You want to see if what you're doing is improving your estimated VO2 max.