Smartwatches from tech companies like Apple and Garmin make
it easy to see a number that could reflect how old you are more accurately than
your age: the VO2max, the maximum amount of oxygen that your body can use
during intense exercise.
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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 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 be? In the last five months, when I fell down a
VO2max rabbit hole, I 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 out celebrating my birthday, my Apple Watch delivered the
most unwanted gift: a notification of a high heart rate. That led me to look at
my VO2max, which the Apple Watch said was 32, well below average for a man in
his late 30s.
In search of a quick solution, I bought a membership at a
high-intensity interval gym, a type of training that specializes in boosting
cardio 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 shy of average, and a Garmin watch
that I also wore rated me at 45.
All that was left to do was to take a real VO2max test, so I
found one. This is where the good news ends. A few hours after pedaling on an
exercise bike with an oxygen mask strapped to my face, I got my lab results:
25, a rating of poor, far below the flattering results from the Apple Watch and
Garmin. Devastating.
Dr Ethan Weiss, a cardiologist in San Francisco who has
studied wearable technology for many years, said my experiment underscored the
pros and cons of using smartwatch data to explore health.
Even if the smartwatch numbers were wrong, they were correct in broad strokes, and I was probably better off wearing one than not.
“On the one hand, you can give it credit for kicking you in
the butt to tell you to go work out,” he said. “But on the other hand, now
you’re sort of burned with this real test and like, ‘What do I do with this
number?’”
Fortunately, after studying all the data, learning how the
wearable algorithms work, and talking with health experts, I arrived at a
positive conclusion: Even if the smartwatch numbers were wrong, they were
correct in broad strokes, and I was probably better off wearing one than not.
My experience can serve as a template for anyone trying to
have a healthy relationship with technology tracking many types of health data,
from sleep patterns to body fat.
A deeper look at the dataLast month, my gym in Oakland, California, called Sweat, announced
that it had teamed up with PNOĒ, a metabolic health lab, to offer
clinical-grade VO2max testing, so I signed up with gusto.
The purpose of a clinical VO2max test is to measure your
maximum oxygen intake at the point that you reach exhaustion. This metric — the
ability for a person to breathe in oxygen and produce carbon dioxide during
exercise — is a strong indicator of cardiovascular fitness.
At Sweat, the gym’s owner, Cassie Hecker, strapped an oxygen
mask over my face and a heart monitor to my chest. She instructed me to pedal
on an exercise bike for about 12 minutes, increasing the intensity each minute
while her equipment gathered data. After I reached my maximum heart rate of 182
beats per minute and began to struggle from exhaustion, the test was done.
The test was very different from the way the wearables
estimated my VO2max. The Apple Watch and Garmin study your heart rate and
movement while you are walking or running for at least 10 minutes and tally a
score.
Spokespeople for Apple and Garmin referred to documents
describing their methods. To inform their algorithms on how to make these
estimates, Apple and Garmin ran 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 are not actually
measuring your oxygen intake and, therefore, are not actually measuring your
VO2max.
“It’s at best an imputed VO2max,” Weiss said. “Not only do
you not have an oxygen mask, you’re not actually exerting yourself to
exhaustion.”
A simple reason that my wearable estimates were so far off
from my real VO2max result is that the way my body works does not match the
heart-rate and oxygen-intake patterns of participants in the Apple and Garmin
studies. Such is the danger of putting too much trust in algorithms.
That left me with no choice but to embrace the hard truth:
My VO2max result in the lab test was very low. But that statistic was only one
data point. The report also showed many positives, including a very high
metabolic rate and fat-burning efficiency and healthy breathing patterns.
Whether you are using devices to measure your progress in losing weight, getting more sleep, or taking more footsteps, what you need to know is whether the numbers are going up or down.
Taking all this information together, Hecker said she rated
my fitness level “average”, higher than the Apple Watch’s cardio fitness rating
of “below average”. She instructed me to focus on my cardio training.
(Admittedly, in the gym classes I pushed myself harder in exercises I enjoyed,
like weight lifting, and tended to take it easy on the cardio exercises I found
torturous, like burpees.) Not doom and gloom.
Ignore the numbers; follow the trendsIn the end, all the health experts I interviewed agreed that
even though the wearable data — much of it flawed — had given me anxiety, I had
reached a net positive. The Apple Watch nudged me to pay closer attention to my
health, and as a result I am healthier now.
The broad trends shown by the wearables were accurate:
Months ago, after the pandemic had taken a toll on my body and mind, I was in
my worst shape in years, and the watch numbers were low. Now, even though the
watch numbers are too high, I do look and feel better, and that is all that
really matters.
That might be the best way to approach wearables — view them
as a directional arrow rather than a precise measuring tool, said Steven Adams,
a sports medicine doctor and personal trainer in Danville, California.
Whether you are using devices to measure your progress in
losing weight, getting more sleep, or taking more footsteps, what you need to
know is whether the numbers are going up or down. But do not take them too
seriously, because all sorts of factors could be throwing them off — a loose
wrist strap, a faulty sensor or, as in my case, imperfect algorithms.
“It’s the trend that’s important, not the absolute number,
because this stuff’s not accurate,” Adams said.
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