When most people think about getting a good night’s rest, they think about the length of time they sleep. But so much more goes into a night of good-quality sleep than just eight straight hours.
Helping you understand the true quality of your sleep is where sleep trackers come in.
Sleep trackers keep tabs on a variety of biological metrics, delivering invaluable data that can help you better understand your sleep patterns, challenges, and areas of potential improvement — all of which you can use to get better, deeper rest, if you understand what you’re seeing.
“Sleep metrics can give people a better understanding of their sleep patterns and peculiarities,” says Dr. Po-Chang Hsu, who specializes in neurology, pediatrics, and neonatology. “This info can help them identify any sleep issues and what lifestyle habits or underlying conditions might be causing them. Consequently, sleep metrics can help people improve their sleep by helping them change their habits, adopt new sleep hygiene, or tackle any other underlying issues.”
But how, exactly, do you use those metrics to get better sleep?
Here are some of the key things your sleep tracker is telling you — and how to use those insights to improve your sleep quality and get more (and better!) rest:
HRV
One of the key things your wearable fitness watch or sleep tracker can monitor is HRV. It’s also one of the least-understood metrics.
“HRV stands for heart rate variability — and is a measure of the variation in time between each heartbeat,” says Chelsie Rohrscheib, Ph.D., neuroscientist and head sleep expert at a wearable sleep technology company called Wesper.
That variability, Rohrscheib explains, comes from the sympathetic nervous system (which increases our heart rate to deal with stress or high levels of activity) and the parasympathetic nervous system (which slows down the heart rate during periods of rest or digestion) working together to keep the heart beating at the optimal rhythm in any given situation.
There’s no one-size-fits-all “perfect” HRV — things like age, gender, and lifestyle can affect your HRV. Younger people, athletes, and men tend to have higher HRV, with the average declining over time. “On average, healthy individuals’ HRV varies between 60 and 65 during wakefulness,” says Hsu. “The healthy sleep HRV should be 20 to 30% lower than the waking numbers.”
How to use HRV to get better sleep
The best way to use HRV to improve sleep quality? “People can watch how their HRV changes every day … then, they can adjust their behavior to improve their HRV score and sleep quality,” says Hsu.
For example, if you have a low HRV, that could indicate that you need to adjust your habits — examining your activity levels, nutrition, or other habits. Generally, low HRV means you’re spending too much time in “fight-or-flight mode” and your sympathetic nervous system is more active than parasympathetic, causing issues with sleep. In that situation, you might practice meditation or breathing exercises throughout the day or before bed — then check your HRV the following morning to see if making the extra investment into relaxation paid off in your sleep quality.
The point is, “HRV data can help people track what habits cause sleep issues and eliminate those habits to achieve healthier slumber,” says Hsu.
Sleep stages
Another key metric for sleep trackers is sleep stages — or, more specifically, how long you spend in each sleep stage over the course of the night.
There are four stages of sleep: Stage 1 non-REM sleep (which happens right as you fall asleep), Stage 2 non-REM sleep (also known as light sleep), stage 3 non-REM sleep (deep sleep), and REM sleep. The percentage of time you spend in each stage shifts as you go through sleep cycles over the course of your sleep. And how long you spend in each stage has a huge impact not only on the quality of your sleep, but on your overall health and wellness.
“Each sleep stage is important for accomplishing different biological functions in the brain and body,” says Rohrscheib. “Deep sleep, for example, is the stage most responsible for the restorative functions of sleep, like repairing cells and tissues, releasing hormones, strengthening the immune system, and clearing the brain of toxic wastes. REM sleep is essential for memory consolidation and emotional processing.”
Your sleep tracker will tell you what percentage of your sleep time you spent in each stage — as well as how that percentage compares to the target for that stage (although the “ideal” target will vary from person to person).
“Humans spend approximately 75% of their sleep in non-REM stages 1 to 3 and 25% in REM sleep,” says Rohrscheib. “However, the exact time spent in each stage is highly variable and dependent on your personal genetics. … If you are feeling well rested, it's likely you spent enough time in each sleep stage.”
How to use sleep stages data to get better sleep
As mentioned, there is no universal “right” amount of time to spend in each sleep stage. Instead, review your sleep tracker data during a time period where you’re getting exceptionally good sleep — and work back from that data to figure out the right amounts of time in each stage for you.
“If you consistently feel well-rested, you can use your data trends to set your baseline for each stage,” says Rohrscheib.
Once you have your baseline, whenever you have a night of sleep that’s off that baseline, you can use it to start investigating what behaviors or scenarios threw you off your ideal sleep schedule. For example, if you notice that you don’t get nearly enough deep sleep after spending an afternoon drinking coffee or an evening drinking cocktails, you may deduce that caffeine or alcohol could be preventing you from getting the deep rest you need to feel your best, and adjust your drinking habits accordingly.
Or if you’re losing out on REM sleep, it may be that you’re setting an alarm to go off before you’ve reached your optimal wake-up time, as REM sleep is more concentrated on the back-end of sleep.
Sleep latency
The time it takes you to fall asleep once your head hits the pillow is called “sleep latency” — and it’s one of the most interesting things your tracker can tell you.
In fact, one of the biggest misconceptions about sleep is that you should be able to fall asleep as soon as you get in bed. That’s very inaccurate. While, again, everyone is different, “a healthy person takes around 15 to 20 minutes to fall asleep, on average,” says Hsu. Taking only a minute or two to fall asleep could be a sign that you’re under-rested and need to better prioritize rest.
How to use sleep latency data to get better sleep
The time it takes you to fall asleep is a great indicator of whether or not you’re setting yourself up for great rest at night. Let’s say that you’ve always had a pretty easy time falling asleep — but after looking at your sleep tracker, you realize that it’s taken you nearly an hour to fall asleep for a week straight. In that situation, you’d want to use the data to figure out what you might be doing during the day that’s causing those issues at night. Have you been extra stressed? Have you been scrolling on your phone before bedtime? Have you been drinking alcohol? Whatever you think the culprit might be, try changing it — and then review the data to see if the change made a difference to the quality of your sleep.
Sleep disturbances
Do you feel as if you wake up way more often than is normal? How often you wake up in the middle of the night is an important piece of sleep data for a couple of reasons.
One is that tracking your sleep disturbances may actually bring peace of mind. Many people exaggerate their overnight awakenings, fearing they’re causing more damage than they really are, so being able to see brief awakenings in context can help assuage worry.
As for sleep disturbances, waking up two to three times a night is considered normal,” says Hsu.
More awakenings than that, and for prolonged periods of time, could indicate a problem with your sleep or sleep space.
How to use sleep disturbances data to get better sleep
If your numbers are consistently off from these targets, your sleep tracker is trying to tell you that there’s something off with your sleep. By studying your data, you can figure out what, exactly, might be causing your issues with staying asleep.
To improve sleep, “[people] can match this data with their daily habits and figure out what behaviors may negatively affect their sleep offset and duration, or cause nighttime disturbances,” says Hsu.
Awakenings can indicate an issue with your sleep environment, including excess light or noise, or a temperature that’s too warm or cool, as well as suggesting needed tweaks to your daytime routines.
Sleep efficiency
You may notice a percentage in your sleep tracker for “sleep efficiency.” This number is a simple calculation of the percentage of time you spent actually sleeping out of the time you spent lying in bed overall. If you climb into bed and read for an hour or two before drifting off, or you wake up overnight for a lengthy amount of time each night, or you laze in bed on quiet mornings, your efficiency percentage may be lower. If your percentage is too high, though — say 98% or 99% — it may indicate that your body is sleep-deprived, and that you’re not spending enough time in bed.
Generally, a sleep efficiency of 85% to 95% is a target sweet spot.
How to use sleep efficiency data to get better sleep
If your sleep efficiency is too low, one of the best pieces of advice is to get out of bed. Tossing and turning as you fall asleep or try to get back to sleep, or lazing in bed all morning, could be triggering your brain to lessen the Pavlovian association of sleep with your bed. Get out of bed and do something calming, so that you can return to bed once you’re truly drowsy and ready for sleep.
On the contrary, when sleep efficiency is too high, it may be a sign that you’re not devoting enough time to sleep. Try to wind down sooner and allow yourself to get the amount of sleep you need. By evaluating the amount of sleep you achieve before days when you feel best rested, you’ll figure out the amount of sleep that is best for you.
“Sleep duration varies depending on age, but the general recommendations are for around seven to eight hours of continuous sleep,” says Hsu.
Don’t get too caught up in any single data point
Clearly, there’s a lot your sleep tracker is trying to tell you — and all of those data points are extremely important in understanding how you’re currently sleeping and how you can improve.
But while it’s important to track your different sleep metrics, it’s also important not to get too hung up on any single not-so-great metric (particularly if it’s the exception, not the rule) — and instead, focus on getting better sleep over time.
“It's important to note that you should never go off of a single test — but instead, rely on how your data trends over time,” says Rohrscheib. “It's completely normal to have a bad night of sleep every once in a while, but you should be aiming for consistently good sleep over weeks and months.”
