Oura’s Chief Scientist Hannu Kinnunen talks shop about your heart rate while sleeping and your night-time heart rate curve, the personal signature your heart draws every night. The Oura ring tracks your night-time heart rate and shows you the heart rate curve in the Oura app.
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 powerful dashboard for interacting with the data the Oura ring tracks.
A lower resting heart rate is a sign of good recovery and health. By looking at your heart rate curve you can also see the effects of circadian misalignment, late meals, late workouts, alcohol or sickness (your heart rate often rises if you have a fever).
Heart rate during the night varies widely between individuals: it can be between 40–100 beats per minute and still be considered normal. It can also change from day to day, depending on your hydration level, elevation, exercise and temperature. As with many of the physiological metrics, such as heart rate variability, it’s often best to compare your heart rate with your own baseline, not with that of others.
From the Oura data we can see that the most common lowest nocturnal heart rate is 55. The lowest night-time HR values range from 35 to 84, with 50% of the people with values between 51 and 60.
Even though there is a lot of variability between individuals, night-time heart rates are very similar for one person – at least when you stick to regular habits. This is why nocturnal heart rate is one of the factors that you may trust when interpreting how your lifestyle choices affect your recovery. For most Oura users, even a 4 bpm change marks a clear difference.
The Oura ring tracks your night-time heart rate continuously during the night with infrared LED sensors. In the Oura app, you can see it in 5-minute sections. When looking at the heart rate curve in the Oura app, pay special attention to these three things:
With these three questions in mind, here are three patterns you may recognize in your own nocturnal heart rate curve.
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 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.
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 the following day. 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 sleep, your airways may actually inhibit the airflow to your lungs. It can also be a sign of your sensitivity to some foods and nutrients. An elevated heart rate may be linked to elevated blood pressure and a decrease in the restorativeness of your sleep.
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.
Don’t have the tools for tracking your night-time heart rate? Until April 30, we’re offering a special pre-order price for the new Oura ring.