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Why Focus on Sleep Debt, Not Quality
You can't track brain activity with a watch.
What is sleep quality?
To date, there is no objective measurement of sleep quality widely agreed upon by sleep scientists. The gold standard questionnaire for sleep quality, called the Pittsburgh Sleep Quality Index, has 7 different types of self-rated questions. Those are subjective sleep quality, the time it takes you to fall asleep (sleep latency), how long you sleep, how much time you spend awake at night, sleep disturbances, sleep medication use, and how you feel during the day.
How are you feeling today?
At RISE, we decided to ask you about how you feel because we believe it's what matters most out of all the sleep quality questions. We care more about how you feel than what you think about your sleep. For the vast majority of us, our brains are optimizing our sleep each night, between the different sleep stages, and our job is to not interfere with the natural sleep process.
Waking up from sleep takes 90 minutes for you to become fully alert. This phenomenon is known scientifically as sleep inertia. While we're conditioned to think, from all the marketing that we should feel amazing and refreshed right on wake up, it's not true. By rating how you feel 90 minutes after wake up and knowing your sleep debt, you'll have a useful measure of your sleep quality.
Why don't you track REM, light sleep, and deep sleep?
REM, light sleep, deep sleep don't have an impact on how you're going to feel or perform the next day. There's some fantastic research conducted by sleep and machine learning scientists at Stanford. In essence, they took all of the best "sleep quality" data from polysomnography to figure out if they can predict how you feel in the morning. It turns out; they can't.
You can't track brain activity with a watch.
If you're not wearing polysomnography on your head when they sleep, you're not tracking your sleep stages. If your tracker or app is giving you a sleep quality score based on movement, depth, or something else, they're basing their work on something other than the last 100 years of sleep science.
What would you do with sleep stage data?
Your brain naturally regulates and calibrates sleep stages each night. It is very good at knowing how much of each step your body needs. You can't optimize that process. What you can do is ensure you're getting enough sleep so that your brain has ample time to get its work done. You can also avoid substances that affect your sleep like alcohol, caffeine, and nicotine close to sleep.