Smartwatches from tech companies like Apple and Garmin make it easy to see a number that might reflect how old you are more accurately than your age: the VO2maxthe maximum amount of oxygen your body can use during intense exercise.
The higher your VO2max, exercise experts say, the better your cardiovascular fitness and, potentially, the longer your life. In the past, only serious athletes sought out a traditional VO2max test, which involved wearing cumbersome sensors while exercising inside a lab, but now anyone can get an estimate by wearing a smartwatch and moving around.
Is it good to have access to this kind of information? And how accurate could a wearable device be? Over the past five months, when I’ve fallen down a VO2max rabbit hole, I’ve learned some uncomfortable truths about my health and the limits of smartwatches.
First, let me tell you about my fitness journey. In November, while I was celebrating my birthday, my Apple Watch delivered the most undesirable gift: a high heart rate notification. That led me to look at my VO2max, which according to the Apple Watch was 32, well below average for a man in his 30s.
Looking for a quick fix, I bought a gym membership for high-intensity interval training, a type of training that specializes in improving cardiovascular fitness. Five months and many kettlebell swings and jump squats later, I felt progress. I burned fat, gained muscle, and felt more energetic. The Apple Watch gave me a VO2max estimate of 40, just below average, and a Garmin watch I also wore rated me at 45.
All that was left to do was take an actual VO2max test, so I found one. This is where the good news ends. A few hours after pedaling on a stationary bike with an oxygen mask strapped to my face, I got my lab results: 25, a poor rating, well below the flattering results from the Apple Watch and Garmin. Devastating.
Dr. Ethan Weiss, a San Francisco cardiologist who has studied wearable technology for many years, said my experiment highlighted the pros and cons of using smartwatch data to explore health.
“On one hand, you can give him credit for kicking your ass to tell you to work out,” he said. “But on the other hand, now you’re kind of burned out with this actual test and you’re like, ‘What do I do with this number?'”
Fortunately, after studying all the data, learning how wearable algorithms work, and talking to health experts, I came to a positive conclusion: even if the numbers on the smartwatch were wrong, they were roughly correct, and you’d probably be better off using one. no.
My experience can serve as a model for anyone trying to have a healthy relationship with technology that tracks many types of health data, from sleep patterns to body fat.
A deeper look at the data
Last month, my gym in Oakland, California, called Sweat, announced that it had partnered with PNOĒ, a metabolic health lab, to offer clinical-grade VO2max testing, so I enthusiastically signed up.
The purpose of a clinical VO2max test is to measure your maximal oxygen intake at the point of exhaustion. This metric, a person’s ability to breathe oxygen and produce carbon dioxide during exercise, is a strong indicator of cardiovascular fitness.
At Sweat, gym owner Cassie Hecker put an oxygen mask on my face and a heart monitor on my chest. She instructed me to cycle on a stationary bike for about 12 minutes, increasing the intensity every minute while her team collected data. After I reached my maximum heart rate of 182 beats per minute and began to fight exhaustion, the test was done.
The test was very different from the way wearable devices estimated my VO2max. He apple watch and garmin study your heart rate and movement while walking or running for at least 10 minutes and tally up a score.
Spokesmen for Apple and Garmin referred to documents outlining their methods. To inform their algorithms how to make these estimates, Apple and garmin He conducted studies involving people who were doing a real VO2max test, as well as other exercises, and studied their heart rates and various metrics.
The key word is “estimate”. The watches don’t actually measure your oxygen uptake and therefore don’t actually measure your VO2max.
“It is, at best, an imputed VO2max,” Dr. Weiss said. “Not only do you not have an oxygen mask, you’re not actually pushing yourself to exhaustion.”
One simple reason my wearable estimates were so far off from my actual VO2max result is that the way my body works doesn’t match the heart rate and oxygen intake patterns of Apple and Garmin study participants. Such is the danger of relying too much on algorithms.
That left me with no choice but to accept the hard truth: My VO2max result in the lab test was very low. But that statistic was just one data point. The report also showed many positives, including a very high metabolic rate and fat burning efficiency and healthy breathing patterns.
Taking all of this information together, Ms. Hecker said she rated my fitness level as “average,” higher than the Apple Watch’s cardio fitness rating of “below average.” She instructed me to focus on my cardio training. (Admittedly, in gym class I put more effort into exercises I enjoyed, like weight lifting, and tended to take it easy in cardio exercises I found torturous, like burpees.) It was not pessimism.
Ignore the Numbers; follow the trends
In the end, all the health experts I interviewed agreed that while portable data (many of it flawed) had caused me anxiety, it had achieved a net positive result. Apple Watch encouraged me to pay more attention to my health, and I am now healthier as a result.
The general trends that wearables showed were accurate: months ago, after the pandemic took its toll on my body and mind, I was in my worst shape in years, and clock numbers were down. Now, even though the clock numbers are too high, I look and feel better, and that’s all that really matters.
That may be the best way to approach wearables: View them as a directional arrow rather than a precise measurement tool, said Steven Adams, a sports medicine physician and personal trainer in Danville, California.
Whether you’re using devices to measure your weight loss progress, getting more sleep, or taking more steps, what you need to know is whether the numbers are going up or down. But don’t take them too seriously, because all sorts of factors could be throwing them out of balance: a loose wrist strap, a faulty sensor, or, as in my case, imperfect algorithms.
“It is the trend that is important, not the absolute number, because this is not exact,” said Dr. Adams.
