Fitbit's New 'Sleep Score', and What It Means

I've been a Fitbit user from the get-go, and it's never been about tracking my steps. Sure, the gamification of the everyday elements of life would kick in from time to time, and my wife and I would occasionally do laps around our apartment simply so we could get to whatever our Fitbit goal for the day was, but the part of the tracker data that I was always most interested in was the sleep tracker.I've been a Fitbit user from the get-go, and it's never been about tracking my steps.  Sure, the gamification of the everyday elements of life would kick in from time to time, and my wife and I would occasionally do laps around our apartment simply so we could get to whatever our Fitbit goal for the day was, but the part of the tracker data that I was always most interested in was the sleep tracker.

And now, Fitbit has unveiled the next step in the gamification of sleep: The Sleep Score.

Here are my Sleep Score numbers from the past seven nights: 59, 69, 67, 61, 59, 70 and last night's Sleep Score of 56.  But what the hell does that mean?

On the October 28 episode of The Snooze Button Podcast, I talked with Dr. Conor Heneghan, Lead Sleep Researcher at Fitbit, to get the details on what Sleep Score is all about.

"The Sleep Score,' he says, "was basically to respond to customers who were saying, 'we love all the detail you give us.'"

"As you know, on a Fitbit device you can measure your duration of sleep, how often you woke up, how much light sleep, how much REM sleep. So there's a lot of data and you know, it's fascinating. It's great to look at the graphs. And people said, 'Hey, can you give me a single number that will summarize it all? So I know - roughly speaking - what was my overall quality of sleep for that night?'"

As I suggested, the Sleep Score number is simple - a number, out of one hundred, that serves as a general indicator.  However, the simplicity of the number belies the heavy-duty math and science that go into the calculations.

"We look at three major aspects of your sleep," Conor explains.  "Still, the most important thing is 'how much did you actually sleep'. So the total sleep time is 50% of your score."

In my own case, I slept last night for 4:11; but I had about 25 little red lines in the graph, showing all the times I woke up.  Those periods of wakefulness added up to 51 minutes, contributing to a score of 25/50 in the Time Asleep category.

"The second part of the sleep score, which is 25% of the score" he continues, "is the relative distribution of your deep and your REM and your light sleep. So as you've probably picked up from your own reading experience, deep sleep is very important because it's where you have physical restoration, you get human growth hormone secreted more during that period than any other.  So sleep scientists in general recommend getting as much deep sleep as you can as a good thing. Typically between 10 and 20% of your sleep will be that particular form of sleep."

"REM sleep is also important," he says.  "REM sleep, which is also known as 'dreaming sleep' is also critical primarily for mental function. And in that case, it's kind of a sweet spot, which might be between say 15 and 25% of your night. So what we do with our Sleep Score is we look to see where you fit in those ranges relative to your age and gender. And if you're in the kind of the optimal zones, we award the maximum marks."

Back to my numbers from last night, then.  My Fitbit Versa 2 says I got about half an hour of REM sleep (10%) and 25 minutes of deep sleep (9%).  Way below where I'm supposed to be.  No wonder it only contributed 15 points toward my total Sleep Score.  The last section is something called "Restoration".  So what's up with that?

"What we did there is over the last few years, we've experimented with various physiological metrics to see how they correlate with your sleep quality," Conor explains. "What we discovered is that basically in the ideal world, your heart rate would slow down at nighttime to near its sort of base rate. However, if you're stressed, or if, you've had too much caffeine or too much alcohol, your heart rate will often be elevated during that during the night.  And that leads to poor sleep quality in our experience. So part of the restoration score is your heart rate, during the night. The second part of your restoration score is the amount of movements during the night. So, if you move a lot during the night, it's typically giving you what are called autonomic arousals, [and] you're not quite getting into the deeper states of sleep. So we're looking for the large movements during sleep combined with your heart rate during sleep and come up with a restoration score."

For me?  I spent 12% of my night tossing and turning.  That's actually good for me - if you have a listen to the episode of The Snooze Button Podcast that featured my sleep specialist, Dr. Mark Boulos from Sunnybrook Hospital in Toronto, you'll hear the full explanation of how much I was flailing about in my sleep.  And 37% percent of my night was spent with my heart rate below a base rate of 62bpm.  Decent.  And gives me a better understanding of where those 16/25 points came from.

So overall, my Fitbit Sleep Score last night was 56 - a number Fitbit describes as "Poor".

"The typical Fitbit user is hovering around about 75," Conor says - and adds cheerfully, "we don't want it to be an exam."

When I ask about the gamification of sleep, and whether he thinks people will stress over the new numbers, he suggests those people might be missing the point.

"We're not expecting people to get a hundred every night," he cautions. "What we really want to do is to tell people, 'find out your own pattern.' If you're a person whose average is 70, that's fine, but then you can experiment yourself so you can experiment to see, do I do better if I go to bed at the same time? Do I do better if I exercise in the evening? Do I do a better exercise in the morning? We want to get out tools for people to kind of play around with their own sleep quality."

And for the record: Conor's own Personal Best for his Sleep Score is 89.  So don't aim too high.  (The guy's been studying sleep for decades.)

He also cautions that these scores are meant as a general indicator for people who'd be considered "normal" sleepers, which echoes the conversation I had with Dr. Michael Grandner about the accuracy and efficacy of sleep trackers in general.

The best way to get the full impact of the conversation is to hear it in the context of the full episode.

HEADS UP:  No, Fitbit didn't pay anything for this episode.  They DID contribute a "review copy" of a Fitbit Versa 2, which - as you'll hear in the full interview - I'm going to use as the basis for the portion of this experiment where I ask the question, "Did this or that solution actually impact my sleep."  Dr. Michael Grandner says a Versa 2 is accurate enough to tell me if various things and making an actual difference in my sleep.   And like I said, I've been a Fitbit customer since Day One anyway.