Smartwatches from tech companies like Apple and Garmin make it easy to see a number that reflects your age more accurately than your actual age: VO2maxthe maximum amount of oxygen your body can use during intense exercise.
Exercise experts say that the higher your VO2max, the better your cardiovascular fitness and, potentially, the longer you will live. In the past, only serious athletes would seek out traditional VO2max testing, which required wearing bulky sensors while exercising in a lab, but now anyone can get an estimate by walking around with a smartwatch.
Is it okay to have access to this kind of information? How accurate are wearables? Over the past five months, as I fell down the VO2max rabbit hole, I’ve learned some uncomfortable truths about my health and the limitations of smartwatches.
First, let me tell you about my fitness journey. When I was out celebrating my birthday in November, my Apple Watch delivered the most unwelcome gift: a high heart rate notification. This led me to check my VO2max and the Apple Watch reads 32, well below the average for a man in his 30s.
Looking for a quick fix, I bought a membership at a high-intensity interval gym, a workout that specializes in improving cardiorespiratory fitness. After five months, after many kettlebell swings and squat jumps, I feel improved. I burned fat, gained muscle, and felt more energized. The Apple Watch gave me a VO2max estimate of 40, which was slightly below average, while the Garmin watch I also wore gave me an estimate of 45.
All that was left to do was to do a real VO2max test, so I found one. This is where the good news ends. After a few hours on the exercise bike with an oxygen mask strapped to my face, I got the lab results: 25, a poor rating, well below the satisfactory 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 highlights the pros and cons of using smartwatch data to explore health.
“On the one hand, you can trust it to kick your ass to get you to work out,” he said. “But on the other hand, now you’re kind of burned by this real test, like ‘what am I going to do with this number?'”
Luckily, after studying all the data, learning how wearable algorithms work, and talking to health experts, I’ve come to a firm conclusion: Even if the smartwatch’s numbers are wrong, they’re mostly right, and I Better to wear one than not.
My experience can serve as a template for anyone trying to forge a healthy relationship with technology that tracks many kinds of health data, from sleep patterns to body fat.
Drill down into the data
Last month, my Oakland, CA gym called Sweat announced a partnership with metabolic health lab PNOĒ to offer a clinical-grade VO2max test, so I signed up with gusto.
The purpose of the clinical VO2max test is to measure your VO2max at exhaustion. This measure—a person’s ability to take in oxygen and produce carbon dioxide during exercise—is a strong indicator of cardiovascular fitness.
At Sweat, the gym owner, Cassie Hecker, put an oxygen mask on my face and a heart monitor on my chest. She instructs me to ride the exercise bike for about 12 minutes, increasing the intensity every minute while her device collects data. The test was done after I hit my maximum heart rate of 182 bpm and started to struggle with exhaustion.
This test is very different from how the wearable estimates my VO2max.this apple watch and Garmin Study your heart rate and movement and calculate a score while you walk or run for at least 10 minutes.
Spokespeople for Apple and Garmin referred to documents describing their approaches.To inform their algorithm how to make these estimates, Apple and Garmin Studies have been done on people doing real VO2max tests as well as other workouts and looked at their heart rate and various metrics.
The key word is “estimate”. These watches don’t actually measure your oxygen intake, so your VO2max isn’t actually measured.
“It’s an estimated VO2max at best,” Dr. Weiss said. “Not only are you without an oxygen mask, but you’re not actually exhausting yourself.”
One simple reason why my wearable estimates were so far off from my true VO2max results was that the way my body worked didn’t match the heart rate and oxygen intake patterns of Apple and Garmin study participants. This is the danger of putting too much trust in algorithms.
This left me with no choice but to accept the brutal fact that my VO2max results in lab tests were very low. But that statistic is just one data point. The report also revealed a number of positives, including a very high metabolic rate and fat burning efficiency as well as a healthy breathing pattern.
Putting all this information together, Ms. Hecker said she rated my fitness level as “average,” above the Apple Watch’s “below average” aerobic fitness level. She directed me to focus on cardio training. (Admittedly, in PE class, I work harder on the exercises I love, like lifting weights, and tend to relax on some of the cardio that I find grueling, like burpees.) Not doom and gloom.
Ignore the numbers; follow the trends
In the end, all the health experts I interviewed agreed that while wearable data — most of which are flawed — made me anxious, I had reached a net positive. Apple Watch has made me pay more attention to my health and I am healthier as a result.
The general trend shown by the wearables is accurate: a few months ago, after the pandemic took its toll on my body and mind, I was in the worst physical shape in years and had a low number of watches. Now, even though the watch number is too high, I do look and feel better, and that’s what really matters.
That’s probably the best way to approach wearables—think of them as directional arrows rather than precise measurement tools, says Steven Adams, a sports medicine doctor and personal trainer in Danville, Calif.
Whether you’re using a device to measure your progress in losing weight, sleeping more, or taking more steps, all you need to know is whether those numbers are going up or down. But don’t take them too seriously, as a variety of factors can cause them to fail — a loose wristband, a faulty sensor, or, like me, an imperfect algorithm.
“It’s the trends that matter, not the absolute numbers, because these things are not exact,” Dr. Adams said.
