By Dr. Mercola

If you ask Sy Perlis, who broke a weightlifting record at the age of 91, or Tao Porchon-Lynch, who won ballroom dance competitions and taught multiple yoga classes a week at age 94, your chronological age really is just a number.

How your body and mind work at the age of 60, 70, 80, and beyond is the result of a small part genetics and a large part lifestyle habits, particularly those that have persisted over the years.

It can therefore be difficult to estimate your longevity based on your chronological age alone, as someone in their 80s could easily be healthier than someone in their 70s, depending on their diet, exercise habits, and outlook on life.

A better indicator of longevity than your chronological age, according to researchers at the Norwegian University of Science and Technology, may be your fitness age.

Your Fitness Age May Predict Your Lifespan

Fitness age is based on the concept of VO2max, which is the maximum amount of oxygen you can take in while exercising. Your VO2max can be used as a measure of cardiovascular endurance; if yours is below average compared to other people your age, it means your fitness age is actually greater than your chronological age.

On the other hand, a better-than-average VO2 max could mean your fitness age is younger than your age in years. Even better, it's possible to improve your VO2 max, which means your fitness age can actually get younger as you get older…

The primary problem with using VO2 max to gauge your longevity is that very few people know what theirs is, and finding out typically requires high-tech testing on a treadmill.

The Norwegian researchers, however, were able to develop an algorithm based on the aerobic capacity, waist circumferences, heart rate, and exercise habits of nearly 5,000 people. This has yielded a method for estimating, quite accurately, a person's VO2 max.¹

Next, the researchers explored whether or not VO2max actually correlated with lifespan. They analyzed the VO2max, fitness age and chronological age of more than 55,000 adults and found a strong association.

Those with the worst readings for VO2max (85 percent or more below the average for their age, which means they had a high fitness age) had an 82 percent higher risk of dying prematurely than those whose fitness age was the same as, or lower than, their chronological age.²

The authors believe that fitness age may predict premature death better than risk factors like overweight, high blood pressure, or smoking.

Use This Online Calculator to Determine Your VO2max and Fitness Age

You're probably curious what your fitness age is. Fortunately, the Norwegian researchers have refined and updated their online calculator for determining fitness age.³ This year, I turned 60, but my fitness age according to this calculator is half that -- 30 years old.

By inputting just a bit of information (such as your age, gender, waist size, height, and exercise habits), it will estimate your level of fitness, giving you both your VO2max and fitness age.

If you don't like what you see, the good news is that you can change it. Lead researcher Ulrik Wisloff, professor at the K.G. Jebsen Center for Exercise in Medicine at The Norwegian University of Science and Technology, said "Thankfully, fitness age can be altered," and if your fitness age is not as low as you would like "just exercise."⁴

Exercise in Your 20s Might Improve Your Brain Function in Middle Age

Researchers at the University of Minnesota highlighted the strong link between exercise, heart health, and brain health at all points of your life. They examined data collected over a 25-year period from 2,700 US adults, concluding that those who had greater cardiorespiratory fitness in their teens and 20s scored better on cognitive tests in their mid-40s and 50s.⁵

For each additional minute spent on the treadmill during the initial test, he or she was able to accurately recall 0.12 more words at follow-up 25 years later. Those who were fitter in their early adulthood also scored better on tests designed to assess reaction speed and the mental agility needed to answer trick questions.

The impact of fitness was deemed to be independent of other dementia-related risk factors such as diabetes, high cholesterol, and smoking. The good news is that if you were fit in your 20s, it's likely to have lasting benefits. But if you weren't, you may feel slightly defeated… don't.

Among those who weren't the most fit in their 20s, but who improved their fitness level in the decades that followed, their scores on the cognitive tests were higher than those whose fitness levels remained the same or got worse. So it's truly never too late to start exercising. Even if you've never exercised a minute in your life, you can start today and immediately begin to experience the benefits.

Those who exercise the most tend to have the least amount of brain shrinkage over time. Not only that, but exercise actually causes your brain to grow in size. In one study, adults aged 60 to 80 who walked for 30 to 45 minutes, three days per week for one year, showed a 2-percent increase in the volume of their hippocampus⁶—a brain region associated with memory. This is one of the reasons why I recommend getting a fitness tracker and making sure you walk about 7-10,000 steps a day, not as your only exercises, but in addition to your regular exercise program.

The Sitting-Rising Test Might Also Predict Longevity

If you want to try another quick tool to measure your level of fitness, try the sitting-rising test (SRT). Sit down on the floor, and then get up, using as little assistance from your hands, knees, or other body parts as possible. For each body part that you use for support, you'll lose one point from the possible top score of 10.

For instance, if you put one hand on the floor for support to sit down, then use a knee and a hand to help you get up, you'll "lose" three points for a combined score of 7. What do the numbers mean? They correlated strongly with participants' risk of death during the study period of just over six years. For each unit increase in SRT score, participants gained a 21 percent improvement in survival. Specifically:

• Those who scored 0-3 were 6.5 times more likely to die during the study than those who scored 8-10
• Those who scored 3.5 to 5.5 were 3.8 times more likely to die
• Those who scored 6 to 7.5 were 1.8 times more likely to die

While I wouldn't take the results of this study as "gospel" and become distressed if you are 30 years old and score a three, it does provide an interesting perspective on the connection between mobility and health and can provide encouragement for many to get back in shape – especially if you score poorly on both the SRT and the fitness age calculator.

How to Improve Your VO2max and Fitness Age

Virtually any type of exercise can improve your VO2max and lower your fitness age. However, one of the most efficient ways to do so is to engage in high-intensity interval training (HIIT). If you use the online calculator for determining fitness age, you'll notice that one of the questions asks about the intensity of your exercise. Reporting that you sometimes "go all out" when you exercise likely improves your fitness age tremendously because it boosts your body's natural production of human growth hormone (HGH), which will help address the muscle loss and atrophy that typically occurs with aging (among other benefits).

Another question asked on the online calculator relates to your resting heart rate, with a lower resting heart rate being preferred for longevity. HIIT, which includes short bursts of high-intensity activity followed by periods of recovery, has been found to improve both VO2max and resting heart rate – even if you start after the age of 40!

HIIT Started After Age 40 Improves VO2Max

A study presented at the May 2014 EuroPRevent meeting in Amsterdam, The Netherlands, found that men who begin intensive exercise after age 40 get similar benefits to those who started prior to age 30 – as well as show several health advantages compared to men who do not exercise.

For instance, both exercise groups (those who started prior to 30 or after age 40) had resting heart rates of about 57-58 beats per minute, much lower than the men who did not exercise (who had resting heart rates of about 70 beats per minute). The exercising men also had higher maximum oxygen uptake (VO2max) and similar evidence of exercise-related improvements in heart structure and function. According to study author David Matelot of the French Institute of Health and Medical Research:⁷

"...despite biological changes with age, the heart still seems -- even at the age of 40 -- amenable to modification by endurance training. Starting at the age of 40 does not seem to impair the cardiac benefits… it's never too late to change your way of life and get more physically active. This will always be beneficial for the heart and well-being. And there's no need for a high level of training for many hours a week…"

Just 12 Minutes of Intense Exercise a Week Boosts VO2Max

Spending just 4 minutes a few times a week is all that is needed to engage in HIIT to significantly improve your VO2max and fitness age. That's right – just 12 minutes a week, or four minutes a day for three days was all it took to improve fitness levels in overweight inactive middle-aged men. For the study, one group of men followed a protocol known as 4x4 training, completing four intervals of four minutes of high-intensity exercise (16 minutes a day, the "16-minute group") three times a week for 10 weeks. The second group exercised three times a week using four-minute high-intensity sessions, for a total of just 12 minutes of exercise a week, or just four minutes a day (the "4-minute group").⁸

Both groups showed marked improvements. The 4-minute group had a 10 percent increase in VO2max compared to a 13 percent increase in the 16-minute group. The 4-minute exercisers also experienced decreases in their blood pressure levels at amounts even greater than the 16-minute group. Those who exercised in 16-minute sessions did have greater reductions in cholesterol and body fat than the 4-minute exercisers. However, even 16 minutes of exercise three times a week should be easily attainable by most people. Other research has shown:

• Participants were able to improve their insulin sensitivity an average of 24 percent with as little as three minutes of HIIT per week.⁹
• Four minutes of exercise performed at extreme intensity four times a week may improve your anaerobic capacity by 28 percent, and your VO2 max and maximal aerobic power by 15 percent in as little as six weeks. (For comparison, those who performed an hour of steady cardiovascular exercise on a stationary bike five times a week only improved VO2 max by 10 percent, and their regimen had no effect on their anaerobic capacity.)

HIIT, Super Slow Weight Training, and Daily Walking: Keys for Longevity

Several years ago, Phil Campbell helped me understand the importance of high-intensity exercise and its value in increasing growth hormone for longevity. For a demonstration using an elliptical machine, please see the video above. Here are the core principles:

• Warm up for three minutes
• Exercise as hard and fast as you can for 30 seconds. You should be gasping for breath and feel like you couldn't possibly go on another few seconds. It is better to use lower resistance and higher repetitions to increase your heart rate
• Recover for 90 seconds, still moving, but at slower pace and decreased resistance
• Repeat the high-intensity exercise and recovery seven more times. (When you're first starting out, depending on your level of fitness, you may only be able to do two or three repetitions of the high-intensity intervals. As you get fitter, just keep adding repetitions until you're doing eight during your 20-minute session)
• Ideally, incorporate Buteyko breathing into the workout, which means you do most of the workout by only breathing through your nose (not shown in the video above)
• Cool down for a few minutes afterward by cutting down your intensity by 50-80 percent

Dr. Doug McGuff has helped me understand how super-slow weight training might be an even more superior form of high-intensity training, compared to high intensity cardio. By slowing your movements down, you're actually turning them into high-intensity exercise. The super-slow movement allows your muscle, at the microscopic level, to access the maximum number of cross-bridges between the protein filaments that produce movement in the muscle. You can perform the super-slow technique with many strength training exercises, such as hand weights, resistance machines, bodyweight exercises, or resistance bands.

Ideally, you'd incorporate both versions of high-intensity exercises, as they each provide important pieces of the fitness puzzle. For example, you might do conventional HIIT using a stationary bike once or twice a week, and super-slow high-intensity weight training once a week—or vice versa, to end up with a total of three high-intensity sessions per week. Remember that, as your fitness increases, the intensity of your exercise goes up, and the frequency that your body can tolerate goes down. As a result, you need to continuously customize your program to your own fitness level and other lifestyle issues. As a general rule however, you do not want to do high-intensity interval training exercises more than three times a week.

High-intensity strength training can be done twice a week initially, but as you get stronger you will need more recovery time and eventually drop down to once every 7-10 days. Any more than that and you'll put your body under too much strain. Your body needs time to fully recover in between sessions. Finally, in addition to regular HIIT workouts, try to sit as little as possible and walk as much as you can (ideally 7,000 to 10,000 steps a day). This fitness program, combined with healthy eating, proper sleep and stress management, is key for boosting your longevity at any age.