Many of us experience sleeping problems. Since the quality of sleep of the night before plays a central part in multiple daily functions, no wonder biohackers around the world are looking for ways to track and optimize sleep. To maximize your sleep quality, aim to sleep for 7-8 hours per night.
ACCURACY OF MEASURING SLEEP
In terms of accuracy and user convenience, a sleep tracker placed under the bed sheets is the preferred option. A significant portion of activity meters recognizes the various stages of sleep based on body movements only. These include many activity trackers and smartphone applications. Adding a separate sensor to track the heart rate, body temperature, and respiratory frequency significantly improves the measuring accuracy. There are sleep trackers available that use electroencephalograms; these may be even more accurate.
Activity trackers, sleep rings, heart rate belts, and various headgear may be uncomfortable to use as they may disrupt the optimal blood flow. If you are concerned about electromagnetic radiation, choose a device that is not placed directly on the skin and that can be switched to flight mode during the night. In terms of the electromagnetic radiation risk, it is smart to choose a Bluetooth device with a short-range (0.5–1.0 mW).
HEART RATE VARIABILITY (HRV)
HRV measures stress levels during the night and the body’s response. The activity of the parasympathetic nervous system increases during orthodox sleep while the sympathetic nervous system is more active during REM sleep. To measure HRV during sleep, wear an activity tracker, wearable jewelry such as a smart ring, or a heart rate belt that measures sleep quality. HRV indicates sleep quality in multiple ways. For example, increased heart rate variability (HRV) during the night indicates the activation of the parasympathetic nervous system (RMSSD). Particularly so that heart rate variability’s HF component is sufficiently high (HF increases during the activation of the parasympathetic nervous system). Additionally, constant or decreasing daily resting heart rate (HR) in the morning (compared to the monthly average) indicates good sleep quality.
Sleep alternates between two stages: orthodox sleep and REM sleep. The majority of sleep is orthodox sleep (deep sleep, quiet sleep, slow-wave sleep) that can be further divided into three NREM (non-rapid eye movement) stages: N1, N2, and N3. These are in contrast to REM sleep, or R sleep (paradoxical sleep, rapid eye movement sleep). Sleep quality is considered good when REM sleep represents 20–25 % and deep sleep represents 10–20 % of the time spent asleep. These phases can be distinguished from one another via EEG (electroencephalography). Additionally, it goes without saying that little to no waking up during the night indicates good sleep quality.
BODY TEMPERATURE/ BLOOD PRESSURE
Both your body temperature and blood pressure drop during the night. They are at their lowest at the N3 stage of sleep. During this stage of deep sleep, breathing is stable and EEG readings consist of slow delta waves. If your body temperature and/or blood pressure are higher than normal, it could be a sign of poor sleep quality. In this case, it might be beneficial to look into potential causes for poor sleep (e.g., stress).
Sleep latency can indicate how well you have slept the night before and how well-rested you are in general. Sleep latency can be tested, for example, via the Multiple Sleep Latency Test (MSLT). MSLT is known as the day-time nap test as it measures how fast you fall asleep during the day in a quiet environment. This test takes place in a supervised environment and is often used to test for narcolepsy. You can test your sleep latency at home by taking a nap during the day while holding an object (that doesn’t break easily). When you fall asleep the object will fall to the floor and wake you up. Record the duration of this process with an app on your phone. When falling asleep takes over 15 minutes, it indicates that you are well-rested if it takes shorter than that you might want to track your sleep and see what’s going on.
Since eye movement is different across the sleep stages, measuring eye movements during the night can give an indication of one’s sleep quality. To measure eye movement during sleep, wear a tracker fastened to the head that senses eye movement (e.g., EOG; electrooculography) or measures via EEG (electroencephalogram) signals.
Nocturnal movements (i.e., movement during the night) can indicate the quality of one’s sleep. Your sleep should have periods every night that last at least 15 minutes where there is no discernible movement. Unusual restlessness or movements during the night indicate poor sleep quality. To measure nocturnal movements, for example, wear sleep trackers that sense body movements during sleep using radio waves. Alternatively, you can get an idea of your nocturnal movements from sleep applications that utilize the motion sensors of a smartphone.
It is not always possible to get enough sleep – traveling or a busy work schedule may mean reduced hours of sleep. When this is the case, pay special attention to the recovery of your nervous system (HRV), the time it takes to fall asleep, and the amount of deep sleep in proportion to the total time spent asleep. If the morning resting heart rate begins to creep up, try to organize rest days to boost recovery!
How do you measure sleep quality? Share your tips in the comments!