This post is part ofFind Your Fit Tech, Lifehacker’s fitness wearables buying guide.
When you strap on a fitness wearable, you suddenly have a wealth of data about your own body.
Your goals are probably things like: sleeping better, running faster, losing weight, and staying active.
There are some pretty big leaps between those two categories.
I find it helpful to separate a wearables features into things itmeasuresversus things itestimates.
I like to useMarco Altinis frameworkfor this.
Examples would be heart rate, skin temperature, and movement.
Calculations or estimates of things we could theoretically measure another way.
A lot of the more sophisticated-sounding features on wearables fall into this category.
Its a made-up metric.
We’re left with two questions, then.
First, is a given metricaccurate?
And second, is the metricuseful?That depends on context.
What do you end up changing in your real-world life based on your fitness trackers data?
For example, if you end up getting more sleep or more exercise, thats probably a good thing.
But its easy to end up chasing a made-up metric that doesnt actually benefit you.
Unfortunately, those studies dont happen before devices are released.
They happen after the fact, usually in small numbers and with not enough funding.
By the time theyre published, the companies have moved on and are producing different models.
There is, by definition, no way to validate whether any of the made-up metrics are accurate.
(Some devices are better at this than others.)
But wearables arenotgood at telling the difference between different stages of sleep.
To do that properly, you gotta analyze brain waves, which a wristwatch simply cannot do.
The Oura said I wasnt getting enough REM sleep.
The Whoop said I was getting too much.)
Some devices have gotten impressively good at guessing at sleep stages, but theyre still just guesses.
As a feat of technology: very cool.
As personal data: absolutely not worth paying attention to.
Even if the sleep stages were totally accurate, I still wouldnt bother looking at them.
Because how do you get more deep sleep, or more light sleep, or more REM?
Thats thesame advicethey give to people who want to get more REM sleep.
You get the idea.
Dont trustthe sleep stages or sleep quality scores.
So its reasonable to expect this metric to be relatively accurate.
If you want to be sure youre getting accurate heart rate data,I recommend a chest strap.
But what about those zones?
This is where things get trickier.
If youre training with heart rate, youre probably usingzones.
These calculations are often very wrong.
The formula isnt accurate, either.
Trust recovery metrics like HRV (but not readiness scores)
Do youneedto track your recovery?
Most of us can probably stop there.
I like to look at the numbers.
Resting heart ratetends to increase when youre stressed or sick.
It can spike upwards if you drank alcohol or didnt get much sleep.
It trends downward over time as your cardio fitness improves.
Heart rate variability, or HRV, measures how irregular your heartbeats are.
It also doesnt have a sense of when Iwantto be working harder and taking on more fatigue.
Ive written before aboutthe better way to use your readiness data.
Ignore the scores, and take the measurements in context.
Too bad they arent accurate enough to really fulfill that promise.
As Ive noted before, fitness trackers are notoriously inaccurate at calculating calorie burn.
I find that calorie burn numbers can be useful in the big picture.
What I wouldnt do is nickel-and-dime yourself when it comes to specific numbers.
Your watch isnt accurate enough to support either of those assumptions.
Fueling your body and feeling good are more important than making the numbers match up exactly.
Ultimately,the number of steps you take in a day is not an important number to track.
But its aneasynumber to track.
If you find step counts motivating, feel free to keep tabs on them.
Some will underestimate, some will overestimate, and theyll all track some activities better than others.
I wouldnt worry about those differences.
Just compare the readings you get from day to day from the same equipment.
Trustthe number of steps you get (its not wholly accurate, but it doesnt need to be).
Dont trustthe implication that you oughta hit X number every day to be a healthy or good person.
Use the step count if it helps you, and ignore it if it doesnt.
In short:the higher your VO2max, the better your cardio fitness.
People with excellent VO2max tend to be able to run longer and faster than people with lower scores.
Its just one of the easier-to-measure components of aerobic and athletic abilities.
(Other metrics of cardiovascular fitnessalso correlate with longevity.)
Wearables test cardio fitness in a very different way than a laboratory VO2max test.
Should you compare this number withVO2max charts?
No, because its not a true VO2max.
This is helpful to track your overall mileage and your speedbut there are caveats.
Your watch will probably be a lot more accurate than your phone, too.
But its not going to be perfect.
Those rare glitches can be pretty annoying.
So dont worry too much if your watch tracks a distance thats slightly different from what you were expecting.
Your finish time is the one that counts for your PR.
Trustthe distance and location, with just a tiny grain of salt.
Dont trustrace distances or locations to be accurate to the inch.
A good watch will be more accurate than an older watch or phone, but nothing is perfect.
Wearable brands make a run at bridge this gap with gamification.
But of course its not always that simple.
On the other, the tricks the devices use to encourage consistency can end up backfiring.
Trustthat you will find your own motivation through action.
(If you try, you probably will!)
Dont trustthat the badges and streaks themselves will keep you going.
