Nightly Recharge™ recovery measurement

​Nightly Recharge™ is an overnight recovery measurement that shows you how well you recover from the demands of your day. Your Nightly Recharge status is based on two components: how you slept (sleep charge) and how well your autonomic nervous system (ANS) calmed down during the early hours of your sleep (ANS charge). Both components are formed by comparing your last night to your usual levels from the past 28 days. Your watch automatically measures both sleep charge and ANS charge during the night.

You can see your Nightly Recharge status on your watch and in the Polar Flow app. Based on what we've measured from you, you get personalized daily tips in Polar Flow app on exercise, and tips on sleep and regulating your energy levels on those particularly rough days. Nightly Recharge helps you make optimal choices in your everyday life to maintain overall well-being and reach your training goals.

  1. Continuous heart rate tracking needs to be enabled for Nightly Recharge to function. To enable Continuous HR tracking go to Settings > General Settings > Continuous HR tracking and choose On or Night-time only.
  2. Tighten the wristband firmly around your wrist and wear the watch when you sleep. The sensor on the back of the watch must be in constant touch with your skin. For more detailed wearing instructions, see Wrist-based heart rate measurement.
  3. You need to wear your watch for three nights before you start to see the Nightly Recharge status on your watch. This is how long it takes to establish your usual level. Before you get your Nightly Recharge you can view your sleep and ANS measurement details (heart rate, heart rate variability and breathing rate). After three successful nightly measurements you can see your Nightly Recharge status on your watch.

When your watch detects that you've woken up, it will show your Nightly Recharge status on the Nightly Recharge view. Navigate to the Nightly Recharge view by swiping left or right from the watch face.

The Nightly Recharge status tells you how restorative last night was. Scores for both ANS charge and sleep charge are taken into account when calculating your Nightly Recharge status. Nightly Recharge status has the following scale: very poor – poor – compromised – OK – good – very good.

You can also stop the sleep tracking manually if you watch has not yet summarized your sleep. Already awake? is shown on the Nightly Recharge view when your watch has detected a minimum of four hours of sleep. Confirm by tapping and the watch summarizes your Nightly Recharge instantly.

Tap ANS charge or Sleep charge to see more details.

  1. Nightly Recharge status graph
  2. Nightly Recharge status Scale: very poor – poor – compromised – OK – good – very good.
  3. ANS charge graph
  4. ANS charge The scale is from -10 to +10. Around zero is your usual level.
  5. ANS charge status Scale: much below usual – below usual – usual – above usual – much above usual.
  6. Heart rate bpm (4 h average)
  7. Beat-to-beat interval ms (4 h average)
  8. Heart rate variability ms (4 h average)
  9. Breathing rate br./min (4 h average)
  10. Sleep score graph
  11. Sleep score (1 - 100) A score that summarizes your sleep time and sleep quality into a single number.
  12. Sleep charge status = Sleep score compared to your usual level. Scale: much below usual – below usual – usual – above usual – much above usual.
  13. Sleep data details. See Sleep data on your watch for more detailed information.

You can compare and analyze your Nightly Recharge details from different nights in the Polar Flow app. Choose Nightly Recharge from the Flow app menu to see the details of your last night's Nightly Recharge. Swipe the display right to see the Nightly Recharge details for previous days. Tap the ANS charge or sleep charge box to open detailed view of ANS charge or sleep charge.

ANS charge details in the Flow app

ANS charge gives you information on how well your autonomic nervous system (ANS) calmed down during the night. The scale is from -10 to +10. Around zero is your usual level. The ANS charge is formed by measuring your heart rate, heart rate variability and breathing rate during roughly the first four hours of sleep.

A normal heart rate value for adults can range between 40 and 100 bpm. It is common for your heart rate values to vary between nights. Mental or physical stress, exercising late at night, illness, or alcohol can keep your heart rate up during the early hours of your sleep. It's best to compare your last night's value to your usual level.

Heart rate variability (HRV) refers to the variation between successive heart beats. In general, high heart rate variability is linked to general good health, high cardiovascular fitness and resilience to stress. It can vary greatly from person to person, ranging from 20 to 150. It's best to compare your last night's value to your usual level.

Breathing rate shows your average breathing rate during roughly the first four hours of sleep. It is calculated from your beat-to-beat interval data. Your beat-to-beat intervals shorten when you breathe in and lengthen when you breathe out. During sleep, breathing rate slows down and varies mainly along with sleep stages. Typical values for a healthy adult at rest range from 12 to 20 breaths per minute. Higher values than usual may indicate a fever or impending illness.

Sleep charge details in Polar Flow

For sleep charge information in the Polar Flow app, see Sleep data in the Flow app and web service.

Based on what we've measured from you, you get personalized daily tips in the Polar Flow app on exercise, and tips on sleep and regulating your energy levels on those particularly rough days. Tips for the day are displayed on the opening view of Nightly Recharge in the Flow app.

For exercise

You get an exercise tip every day. It tells you if you should take it easy or go for it. The tips are based on:

  • Nightly Recharge status
  • ANS charge
  • Sleep charge
  • Cardio load status
For sleep

If you didn't sleep as well as usual, you get a sleep tip. It tells you how to improve the aspects of your sleep that weren't as good as usual. Besides parameters we measure from your sleep, we take into account:

  • sleep rhythm over a longer period of time
  • Cardio load status
  • exercise on the previous day
For regulating energy levels

If your ANS charge status or sleep charge is particularly low, you get a tip that helps you get through the days with a lower recharge. They are practical tips on how to calm down when you're in overdrive, and how to energize when you need a boost.

Learn more about the Nightly Recharge in this in-depth guide.