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Like most fit guys, you’re probably addicted to numbers. Chances are you know your max bench and squat, and you might have a pretty good fix...

Turn Back your Body Clock Turn Back your Body Clock

Turn Back your Body Clock

Turn Back your Body Clock

Like most fit guys, you’re probably addicted to numbers. Chances are you know your max bench and squat, and you might have a pretty good fix on your body mass index, too. If you’re super hardcore, you might even know your basal metabolic rate (for the uninitiated, that’s the amount of energy your body churns through when you’re at rest). And no doubt if you’re an endurance guy, you can list your PRs in everything from the 5K to a marathon. But before you get too confident in the story that these numbers tell, especially as they pertain to your long-term health. What is your fitness age? Wait, you don’t know?Your fitness age — even more than your real age — is the key to providing confirmation of your physical prowess or exposing a gaping void at the centre of what you thought was a solid training program. What’s more: Paying special attention to your fitness age, which you can maintain with a very targeted HIIT training regimen, might just save your life years down the road.


Fitness age, which Wisløff introduced to the world in a 2014 study, is rooted in your body’s level of cardiorespiratory fitness (CRF) — its ability to disperse and consume oxygen. In fact, having great CRF — not to be confused with cardiovascular fitness, which refers only to the heart and blood but not the body’s breathing apparatus — is such an important factor to your longevity and your long-term health that a recent scientific statement from the American Heart Association described it as a “potentially stronger predictor of mortality than established risk factors such as smoking, hypertension, high cholesterol, and type-2 diabetes mellitus”. But as Wisløff knows all too well, CRF is difficult to measure — and even more difficult to make sense of once you have it. The surest way of gauging CRF is to calculate your VO2 max, the maximum amount of oxygen you can process during an activity. (The average person has a VO2 max of 30 to 60, with some elite athletes, such as pro cyclists, reaching the 90s.) Since the Nobel Prize-winning Physiologist AV Hill introduced the concept in 1923, the only reliable way to measure VO2 max has been with an exercise test, which asks subjects to push their bodies to exhaustion on a treadmill or a stationary bike while breathing into an ergospirometry system. Even if you endured the process, the larger question remained: What does it even mean? If you’re, say, a 34-year-old guy with VO2 max of 52, how does that inform your health and your training? “When we started this research many years ago”, Wisløff says, “we always told people that they had a VO2 max of 30 or 40 or 50, and then they’d always look at us and ask, ‘OK, well, what is that?’” So Wisløff set off to find a way to do two things simultaneously: 1) easily and accurately calculate VO2 max without the hassle of equipment, and 2) translate the findings into something the average athlete can understand and use to his advantage. Enter fitness age. In 2006 he and his colleagues began conducting an enormous study of cardiorespiratory fitness and other health indicators in 4637 Norwegian men and women, and devised a proprietary formula, which you fill out on his website, that assigns you a fitness age, essentially defined as the average VO2 max of healthy people at any given age. That 34-year-old with a VO2 max of 52? According to Wisløff’s calculations, he’s in fine shape. Generally speaking, the average healthy guy in his 30s has a VO2 max of roughly 49, so the 34-year-old’s fitness age is close to his real age. But he could be doing better, and with the right training regimen, he could easily bring his fitness age down to something on par with a healthy man in his 20s. (Twentysomething males have an average VO2 max of 54.) But if that same 34-year-old found out that he had a VO2 max of 39? Well, he’d have the same fitness age of your typical 60-year-old. He’d be out of shape, with a dangerously elevated risk of developing cardiovascular disease and, according to some studies, cancer and Alzheimer’s. But I know what you’re thinking. “I work out. I run. I lift. Surely my fitness age is super young!” Well, not necessarily. When Wisløff began to measure the fitness ages of his test subjects, he encountered many people who looked fit and worked out but had practically geriatric fitness ages. One group of bodybuilders were lean and muscular, but “their fitness in terms of peak VO2 was very low”, Wisløff says. When he tested amateur endurance athletes — many of whom trained up to 10 hours per week — he also found unexpectedly high fitness ages. That’s because, as Wisløff has consistently found, great CRF is achieved through high-intensity exercise, not long, slow jogging. This has not gone unnoticed by Wisløff’s peers, who believe his greatest accomplishment might not be in creating the fitness-age algorithm — a simple way to estimate VO2 max — but in devising an easy, efficient way to dramatically improve it. Carl “Chip” Lavie, MD, a leading Cardiologist and the author of The Obesity Paradox, told me that he revered Wisløff for expanding “our knowledge of the importance of higher-intensity exercise and its impact on improving fitness and reducing the risk of cardiovascular disease”. When Wisløff pioneered fitness age, he didn’t just create a diagnostic tool; he laid the groundwork for developing what might just be the world’s most useful exercise cure.


You can follow these six tips to boost your body’s cardiorespiratory fitness, bulletproofing your health while leaving plenty of time to do all the activities you love: pick-up hoops, distance running, or improving those max bench and squat numbers inside the power rack. Whatever your goals are, here are the six ways to keep your body young.


What limits the body’s ability to uptake oxygen? We know skeletal muscles weren’t the principal problem — they can handle more blood than they can possibly get. We know that the lungs, while crucial, couldn’t be dramatically altered with training. But the heart is highly trainable, and increasing the heart’s pumping capacity — the amount of blood it can pump in a given amount of time — directly increases the body’s ability to uptake and distribute oxygen. In other words, a more efficient, more powerful heart leads directly to a higher VO2 max. But how exactly do you train your heart to be more efficient and powerful?

Two factors govern pumping capacity: maximal heart rate and stroke volume. Your maximal heart rate is inborn. (What’s the best formula? 211 minus your age multiplied by 0.64.) No matter how hard you train, that number will tick down throughout your life. But you can do a lot to increase the stroke volume of your heart. The heart is like any other muscle. It must be loaded to get trained. And the only healthy way to challenge the heart’s pumping capacity is to fill it with maximal amounts of blood for long periods of time.

The heart achieves maximum stroke volume when it’s pumping at 85–95% of its maximum beats per minute. (For most people, the 85–90% range is sufficient.) So if you want to boost your VO2 max, you’ll want to work out within that range of cardiorespiratory intensity for as long as you possibly can. If you do it right, you’ll end up with an “athlete’s heart”, one that’s bigger, contracts more forcefully, and relaxes quicker. “You’ll have a better motor.”


So how exactly do you get your heart rate to the 85% threshold, and how long can you (and should you) keep it there? It usually takes more than a minute of vigorous exercise before you reach maximum stroke volume. That’s easy enough to do — try running, cycling, or rowing really hard for 60 seconds — but the trickier and more exhausting part is keeping your heart rate and stroke volume locked at that rate. The key to mentally and physically sustaining that kind of workload, is to use interval training. It is obvious that one cannot exercise for very long periods of time at 85–95% of maximal heart rate. “But intervals get you up to that needed intensity” and give you enough rest in between “to get rid of lactic acid that builds up during the interval”.

But not all interval training is equal. Sprint intervals of one minute or less can get your heart rate past the 85% threshold, but they just don’t give your heart enough sustained work at its maximum stroke volume. Tabata training with 20-second maximum-intensity intervals followed by 10 seconds of rest can work, but be aware that your heart rate drops as soon as you stop moving. (And the more fit you are, the faster your heart rate plummets.) If your goal is to improve VO2 max, then it’s better to keep your heart pumping consistently at 85% of its maximum rate than for it to be yo-yoing from 75–100% of its max rate throughout your active workout time.

How long is the ideal stroke-volume maximising interval? In theory, make it as long as possible. (If you can push out 30-minute intervals at 90% of your max heart rate, go ahead and do it. Also, congratulations, your VO2 max is almost certainly spectacular.) It was found that four minutes is a length most can manage. It lets your heart pump at its maximum stroke capacity for an extended time, and it’s sustainable for untrained individuals and beneficial to elite athletes looking to boost their already excellent CRF.

It is recommended program is simple: A 10-minute warm-up, followed by four four-minute intervals of large muscle mass exercise (running, cycling, rowing, swimming) broken up by three minutes of active rest (a very low-intensity version of whatever you’re doing). The results can be dramatic.


Ask a random sampling of men and women to name the kind of athlete with the best cardiorespiratory fitness, and you’ll almost certainly get answers like marathoners, triathletes, and Tour de France cyclists. While this may be true at the elite level, it’s often not the case for weekend-warrior endurance athletes, and the reason is simple: Running, cycling, and swimming for long distances won’t push your heart to its maximal stroke volume, so they won’t do a lot to improve VO2 max if you are already in good shape and go hard for four minutes. “Even these people can improve fitness a lot by exchanging two to three hours of running for periods of 4x4 intervals or even 3x3 intervals.”


You’ve seen those heart-healthy labels at the supermarket, and you know that “eating clean” is a good thing for your health. So can you eat your way to a lower fitness age? Nope. Indirectly, it’s important to have a good diet, because if your diet is better, you adapt better to exercise. “There have been some reports that if you drink beetroot juice or stuff with a lot of nitric oxide in it, that may help your cardiorespiratory fitness — and that may be true with untrained people. But as you get fitter, that supplement doesn’t seem to work a lot.” What about training at elevation or working out on the treadmill with one of those Predator–style hypoxic masks? After all, don’t all the top endurance athletes run high up in the mountains? Wouldn’t just living at altitude boost your VO2 max and reduce your fitness age? Nope again. The science on hypoxic masks is thin. Even though there are some believers out there, I know that world-class endurance athletes in, for instance, some cross-country skiing do not use them. While some world-class endurance athletes travel to high altitudes to train, the effect on performance is tiny. If you’re the thirdbest 800m runner in the world and you want to become the best 800m runner in the world, then by all means move to La Paz, Bolivia (altitude: nearly 12 000 feet). But if you’re something other than an Olympian, you’re going to make the same gains if you do all your interval training in Miami.


It is might expect advised to those looking to reduce their fitness age to do nothing but lungbusting sessions of 4x4 interval training. But such a course would be counterproductive. I can’t just do 4x4. I think it’s totally boring to do just that. In his fitness-age-reducing fitness program, days are reserved for fun runs and 60-minute activities like five-aside soccer. Performs 4x4 interval training only a couple of times per week. The rest of the time, works out like an outdoorsy and not especially fitness-obsessed man. He plays a weekly game of soccer and kayaks. 


By now you’ve probably realised that many popular device-based approaches to improving fitness just don’t pass muster when you’re trying to reduce fitness age. Walk 10 000 steps per day? Why? Your heart rate is never going to get anywhere close to a range where you can lower yourfitness age. Exercise for 150 minutes per week? Sure, that sounds good. But what’s your real output going to be? Heart rate is a better measure,Although this by itself does not mean much, it is a good starting point.