I. Introduction
You’ve always known that exercise is good for you, with wide-ranging benefits not just for how you look but also your health, longevity, performance, mood, and quality of life. But you might be surprised by just how good exercise is for you. In fact, a growing body of research demonstrates that your level of fitness does a better job predicting how long you will live than any other modifiable variable that we know of. Yes, you read that right. Your level of fitness is a stronger predictor of mortality than many other well-known risk factors, including smoking, high blood pressure, high cholesterol, or presence of heart disease.
II. VO2 Max
So how is fitness measured exactly? There are countless methods to quantify someone’s fitness level, but if your goal is predicting longevity a test called VO2 max is clearly the gold standard. VO2 max is a test that measures the maximum amount of oxygen that your body can utilize when undergoing strenuous exercise. Specifically, it is the maximal volume of oxygen an individual can consume in one minute, measured in mL per minute. This value is then normalized to a person’s body weight (a larger person would be expected to utilize a larger amount of oxygen). This is done by dividing the mL of oxygen consumed in one minute by weight in kilograms, which makes mL/kg/min the standard units by which VO2 max is expressed.
The VO2 max is a functional measure of the combined working capacity of your lungs, heart, and muscles. Oxygen is inhaled into the body by the lungs, then transported to where it needs to go by the heart/circulatory system, then utilized by the muscles in the process of producing the energy that is needed to perform work (exercise).
III. How is VO2 max measured?
The most accurate way to measure VO2 max is to measure it directly. This means directly measuring, via a mask, the amount of oxygen consumed during peak intensity exercise. But VO2 max can be measured indirectly through a variety of surrogate methods, some involving exercise, and some involving predictive formulas using metrics such as your age and resting heart rate.
The direct measure of VO2 max is the most accurate and standardized, however it is also the most difficult because it requires the test subject to exercise at maximal intensity, and it requires specialized equipment. The direct method involves an exercise test in which the subject exercises to exhaustion, typically done with a treadmill, exercise bike, or rowing machine. The subject wears a mask which measures how much oxygen they consume and carbon dioxide they expire. After a warm-up period, the subject’s level of exercise effort is slowly ramped higher and higher until the volume of oxygen they consume reaches a plateau. The test typically takes about 15-20 minutes once the warm-up period begins.
An indirect measure of VO2 max can be obtained in a number of ways. With indirect measures the volume of oxygen consumed is not directly measured via a mask, in which case the VO2 max is only an estimation. Indirect measures of VO2 max can be divided into two categories: exercise and non-exercise based estimations.
With exercise based tests, VO2 max is estimated by evaluating exercise performance with a standardized test. For example, VO2 max can be estimated by measuring the subject’s maximal work rate, expressed in watts, on a cycle ergometer. The protocol for this test involves a 5-min warm-up period, after which the workload is increased at a prespecified amount every 2 minutes until the subject reaches exhaustion. This is called a “maximal” test, referring to maximum physical effort, but numerous “submaximal” tests exist as well. In a submaximal test, an individual’s exercise work output is measured at a prespecified submaximal heart rate. Another method is the Cooper 12-minute run test, named after fitness expert Dr. Kenneth Cooper, in which VO2 max is estimated based on how far a person can run or walk in 12 minutes.
Non-exercise based VO2 tests involve calculations that utilize metrics such as age, resting heart rate, and maximum heart rate. Many of these calculations can be found online.
IV. Why is VO2 max important?
Over the last few decades, numerous studies have been conducted in which large populations (sometimes tens of thousands) of research subjects undergo a VO2 max at baseline and then are followed over many years to determine how long they live. Not only are mortality rates calculated, but researchers often study other outcomes such as rates of cardiovascular disease, cancer, or Alzheimer's disease. As a result of these studies, some scientists argue that the VO2 max level is the best single measure of overall health status.[1]
One of the most well-known of these studies was published in JAMA Network Open in 2018.[2] In this study researchers tested the VO2 max at baseline of 122,007 adults (59% men) at an average age of 53 years old. They then divided the group into four quartiles based on their baseline VO2 max test: “Low”, “Below Average”, Above Average”, and “High”. As they followed these groups over time, the Low group had a mortality rate that was nearly 4 times higher than the High group. Furthermore, compared to the Above Average group, the Low group had a mortality rate that was 2.7 times higher, and 1.9 times higher compared to the Below Average group. For comparison sake, note the difference in mortality rates of other well known risk factors in this study: smokers had a mortality rate that was 1.4 times higher than that of nonsmokers, and those with a diagnosis of heart disease had a mortality rate that was 1.3 times higher than no heart disease. These risk factors are important for sure, but they pale compared to the incredible robustness of the impact of VO2 max on our health.
Other large studies have shown that an increase in VO2 max level of 1 MET (which is equivalent of 3.5 mL/kg/min) is associated with a 10% to 20% decrease in mortality rate.[3] An increase in VO2 max level of 3.5 mL/kg/min is highly achievable through a dedicated training program, and in many cases your VO2 max can be increased much higher than this. In addition to mortality rates, VO2 max level has been shown to be highly predictive of other important outcomes, including diagnosis of cancer or Alzheimer's disease.
For those who are not in great shape, there is good news and bad news. First the bad news: as you have probably surmised already, your mortality risk prediction is not as favorable as those who have higher fitness levels. But here is the good news: you have the most to gain from increasing your fitness level. Most of the reduction in risk of mortality and other health outcomes that occurs from increasing VO2 max levels occurs between the least fit group and the next least fit group. In other words, the biggest bang for your buck occurs in going from the lowest category to the second lowest category of VO2 level. In addition, those in the least fit group will experience a larger percentage increase in VO2 max for the same amount of exercise training compared to the higher fit categories. Therefore, you do not need to be in great shape to experience health benefits from improvements in your fitness level. On the contrary, you will experience more benefit the lower your starting level of fitness.
V. How do I improve my VO2 max?
It is estimated that about 50% of your VO2 max score is determined by your genetics, and the other 50% is determined by your level of activity/exercise/training. VO2 max can be increased by at least 15-20% from baseline with a dedicated training program. Any type of exercise, including resistance/strength training, low-to-moderate intensity continuous aerobic training, or high intensity interval training (HIIT), can improve your VO2 max level. This is especially true for those who are starting with a low fitness level at baseline.
But while it’s true that any form of exercise can improve VO2 max, research studies consistently show that HIIT leads to the biggest increases.[4] HIIT programs generally involve repeated, short (3-8 minutes) intervals of near maximum intensity effort, followed by short periods of rest. A HIIT routine can be done with a wide variety of exercises, including running, biking, elliptical, and rowing. A classic protocol, and one that has a considerable amount of research behind it, is the 4x4 protocol. This approach involves exercising for 4 minutes at a heart rate of 90-95% of your maximum heart rate, resting for 3-4 minutes, then repeating for 4 intervals. There are numerous other HIIT protocols that you can find with a quick internet search.
HIIT is an attractive way to train because you can achieve tremendous health benefits in a short amount of time. But don’t let the short time commitment mislead you. HIIT workouts are difficult. Many people find the outside accountability of a coach and/or class helpful to provide the motivation needed to stay consistent with the demanding requirements of a HIIT program. If you are just starting out, it is recommended to spend 3-4 months doing lower intensity aerobic exercise to build up a reserve before starting a HIIT program. Start with one HIIT workout per week. If you build up to 2-3 HIIT workouts per week you are doing really well.
One last recommendation regarding HIIT workouts. Although it is true that HIIT has consistently been shown to be the most effective way to increase VO2 max, it does not stand to reason that your exercise program should consist only of HIIT workouts. There is still very much a role for strength training and low-to-moderate intensity aerobic training. Strength training provides increased muscle mass, increased bone strength, and sets us up to maintain a higher degree of physical function, balance, and stability as we age. Lower intensity aerobic workouts provide the foundation by which we can push our VO2 max higher. An analogy from engineering is that if you are going to build a tall building, you must ensure the foundation is solid. The stronger the foundation (low-to-moderate aerobic exercise), the higher you can build the tower (VO2 max). This is evidenced in that elite athletes in sports that require the highest VO2 max levels spend as much or more time training with longer, moderate intensity cardio workouts than they spend doing shorter, high intensity intervals.
VI. Conclusion:
There are a ton of great reasons to invest in an exercise training program. It’s fun. It keeps us looking and feeling our best. It can be a great social outlet. It’s good for our mood. It’s good for our brain. And on top of all that, it can increase our lifespan as much as anything else we know of. And not only does it increase lifespan, undoubtedly it also increases healthspan. Because we can probably all agree, living longer is not as important as giving those years more life!
[1] Importance of Assessing Cardiorespiratory Fitness in Clinical Practice: A Case for Fitness as a Clinical Vital Sign: A Scientific Statement From the American Heart Association - PubMed (nih.gov)
[2] Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing - PubMed (nih.gov)
[3] Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis - PubMed (nih.gov)
[4] Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials - PubMed (nih.gov)