Michael Martin Cohen, M.D. — One Number Every Sailor Should Know

That number, drumroll please…..…... is your VO2 max. It is one of the best measures of your cardiorespiratory fitness (CRF). But more than just fitness, it also is one of the best measures of your overall health, including your risk for heart attack, stroke, diabetes, Alzheimer’s, as well as your “all-cause” mortality (that is, your likelihood of death from any cause). In fact, it is so important that the American Heart Association has recently recommended that it be considered the 5th vital sign and should be included in everyone’s annual health checkup. [1]

Simply put, VO2 max refers to how much oxygen your body can use during exercise. As active humans we are most concerned with getting the oxygen to our muscles so that we can do our tasks but in reality, there is the chain of events that explains why VO2 max is such a good indicator of overall health. (Figure 1)

1. Oxygen has to get through the lungs and then be transported to the blood vessels

2. CRF requires both sides of the heart be working (right and left ventricles) – systole and diastole

3. The oxygenated blood has to get from the heart to all the blood vessels in the body and the blood vessels have to transport the oxygenated blood to all of the body’s tissues

4. The mitochondria (the cellular energy engine) in the tissues (especially the muscle fibers – myosin / actin – that we’re most interested in) create the energy which allows us to use our muscles – unless we are so fatigued that we can’t.

All things being equal a higher VO2 max is a good thing as it means that your body can take in more oxygen and deliver it quickly to your muscles and other organs, enabling better aerobic performance. Aerobic exercise improves VO2 max significantly. Normal level is between 20 to 60.

So how do we measure it? As discussed in detail in the book [2] measuring O2 and CO2 in the laboratory – Ergospirometry – (Figure 2) is the gold standard for fitness endurance. But it is time consuming and expensive. And for most athletes, including most sailors – even racing sailors – it is not necessary.

Figure 2: Ergospirometry - VO2 max in the lab

Enter the 12-minute run fitness test (Figures 3 and 4) which was developed by Kenneth Cooper, M.D. in 1968. [3] It was an easy way to measure aerobic fitness and was initially validated by the US Air Force. He correlated the 12-minute run test with the treadmill exercise test and found very high correlation. How is the test administered?

Warm up for 5-10 minutes and make sure you are properly hydrated
Use a standard flat surface such as a standard 400-meter outdoor track
Run in the inside lane the entire time
Keep a steady pace and don’t start too fast or you may experience exhaustion
Keep track of the number of laps rounded or the total distance in miles or kilometers in 12 minutes
To calculate VO2max results (in ml/kg/min) use either of these formulas

Here are the norms for men and women:

Another approach is the so-called Rockport Walking Test. This test also compares favorably with the 12-minute run fitness test and the Air Force 1.5 mile running test. [4] All you need is a heart rate monitor (or you can take your own pulse), a stopwatch (or a clock with a second hand), and a level track or a treadmill. (Figure 5)

Figure 5: Rockport walking test measuring pulse

Warm up for 5-10 minutes
Start the stopwatch and immediately start walking as fast as possible – no jogging
At the end of one mile, record your time, e.g. 10.5 minutes
Immediately take your heart rate (multiply x 4 if 15 seconds or x 2 if 30 seconds)

Alternatively, if this all seems to be mathematically challenging, find an online calculator and plug in your weight, age, time, and heart rate. My VO2 max was 36 which is in the Good range for 60+ (I am 72) but I am going to try it again as I was disappointed, and I think I was loafing in the beginning of the test. [5]

The future is wearables. And the future is basically here if you are willing to spend some cash. There are many companies improving their wearable technology year by year. Right now, the best wearables are probably within about 5 points of the true VO2max which is more than good enough for most of us. Garmin (Figures 6 and 7) is one of many companies which have improved year over year.

Using just the wrist to measure VO2max has been a challenge. The best results have generally been with a chest strap as the input device. This particular unit can swing both ways. Other places on the body which work better than the wrist include the forehead and ear. By the time my grandson reads this, undoubtedly every serious athlete will have an implanted device! I’m not going to speculate on where it will be placed. [6]

[1] For a detailed discussion I would refer you to the AHA’s Clinical Statements and Guidelines – 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. Circulation Volume 134, Issue 24, 13 December 2016

[2] Healthy Boating and Sailing

[3] Cooper K. A Means of Assessing Maximal Oxygen Intake Correlation Between Field and Treadmill Testing. Journal of American Medical Association. 1968;203(3):201-204. doi:10.1001/jama.1968.03140030033008

[4] 1 Mile Walk test is a valid predictor of VO2max. Military Medicine June 2011 doi: 10.7205/milmed-d-10-00444

[5] Unless you have been working out, you should clear any increase in exercise level (or test like this) with your Primary Care or cardiologist. Also avoid doing this alone. I will admit that I went down to my home basement gym and did the Rockport walk myself, BUT both of my sons are grown, my mortgage is paid off, and my wife ….

[6] The Apple watch has revamped its health metrics and has included VO2 Max as part of its cardio fitness notifications. How it will compare with Garmin and other high end fitness trackers remains to be seen.