Oura’s Chief Scientist Hannu Kinnunen talks shop about your night-time heart rate curve, the personal signature your heart draws every night if you have the right technology to track it.
Sleep is when your body recovers from the day. The Oura ring tracks your resting heart rate throughout the night and shows you a night-time heart rate curve in the Oura app and Oura Cloud. A lower resting heart rate is a sign of good recovery. By looking at your heart rate curve you can also see the effects of circadian misalignment, late meals, late workouts or alcohol.
Here are three patterns you may recognize in your own nocturnal heart rate curve.
The Hammock: Relaxed in Bed. Ready To Rise.
The hammock-shaped curve can be considered the optimal heart rate curve. During the first sleep cycles, your body relaxes and your blood pressure and heart rate drop. Your lowest heart rate happens at the midpoint of sleep when the amount of melatonin is at its highest. If you are perfectly aligned with the rhythm of the sun, your lowest basal body temperature also occurs around 4 am.
Note that your heart rate can momentarily rise during REM sleep. You can ignore these spikes when looking for the hammock-shaped curve. Towards the end of the night, your heart rate starts to rise to prepare you to wake up. The hammock curve is a sign that your body was relaxed during the night, and ready to rise after a good night’s rest.
The Downward Slope: Metabolism Working Overtime
The Downward Slope is a sign that your metabolism is working overtime. Did you have a late meal, a late workout or a glass of wine before bed? If your resting heart rate starts high and reaches its lowest point right before you woke up, you may wake up feeling unrefreshed. If you see the downward slope regularly, it’s a good time to stop and think if there’s something you could do differently. If you are a late exerciser, doing your physical training session 1–2 hours earlier can be a significant change, for example.
The Dune: Too Tired For Bed
If your heart rate goes up right after you fall asleep, it may be sign that you’re too tired for bed. If it’s past your regular bedtime, you may start feeling the effects of your increased melatonin and lowered blood pressure as your body is trying to inform you about bedtime passing.
Perhaps you went to bed at a different time than usually? Also staying in bed later than normally reportedly leads to lowered cognitive performance. Keeping a steady sleep routine really helps you get better sleep and perform better during the day. There is no single cause for why heart rate starts to increase at the start of the night, but there are some likely candidates: when you relax during the deepest sleep, your airways may actually inhibit the airflow to your lungs. It can also be a sign of your sensitivity to some foods.
Look Inwards for a More Positive Lookout
The night is a mirror of the day. Paying attention to your night-time heart rate curve is a good way to start seeing the physiological effects of your lifestyle. If you find your optimal hammock-shaped heart rate reaction, you can also find a more relaxed, happier, and better performing you.