Heart rate without activity

Evening everyone... I've read discussions about heart rate detection outside of an activity, the device enters a sort of energy saving and the heart rate detection is less frequent, this would lead to an eight estimate... this is saving mode also present on the instinct 2?' 

  • Most Garmin devices, including Instinct 2, have the standard mode with the sampling rate of 15s (and logging 2 minutes averages), the Battery Saver mode (where you can turn the HR sensor off completely), and the Activity mode with sampling and logging mode of up to 1s.

    When you are not active, the sampling rate of 15s is fully sufficient.

  • Unfortunately, in the end it is not enough ... also because very often it tends to underestimate the real heart rate!! Several discussions have been opened on the forum 

  • As I wrote, for the periods of the day, where you are not active, 15s sampling rate is sufficient for the metrics the watch measures. At healthy persons the HR does not change that fast when you are not active. Alternatively you can launch an activity and letting it run all day long, but if you suffer from serious heart problems needing detailed 24/7 monitoring, I would rather recommend getting a medically certified device.

  • What exactly does "15-second sampling" mean? does it detect my heart rate every 15 seconds? because I noticed that he is resting the LEDs flash while during an activity or if I start walking they are instead fixed 

  • Sampling rate of 15s, means that the sensor goes on and takes your HR, once each 15s.

    If you need continuous monitoring with the sampling rate of up to 1s, and do not want to purchase a medical HR monitor, then start an indoor activity (i.e. Cardio), and keep it running all day long (or as long as you need). Of course, the higher usage of the sensor will result in higher power consumption, and the need of more frequent charging.

  • But the sensor is always on!!! Only that during an activity the green light was steady, while in everyday life it flashes ... often it happened to have a real heart rate of 80-90 beats and the slide instead also showed 60-70 bpm, had a sampling taken after 15 seconds should have aligned to the real value 

  • I think there are three different levels of sampling.

    The sensor itself must have its own optical sensing rate to "constantly" measure capillary volume and recognize cycling of that to infer individual pulses. Different sampling rates here would have to be multiple times per second in order to recognize typical heart rates. The 24/7 monitoring is probably using a lower optical sampling rate which is why it looks like it is blinking and why it can fail to measure some very high rates. All of that is just happening in the little controller very close to the sensor. It can save power by firing the little green LED less frequently and perhaps by running its own controller at a slower speed too.

    The main software of the watch is not running this fast to look at individual beats. Instead, it is going to get an averaged figure out of the sensor periodically. This is likely where a "15 second sampling rate" comes from. Reducing this rate can save power by not running software on the main watch as frequently. But it also likely means they just run a counter in the sensor and know how many beats since the last check, without any idea if the beats were bursty or evenly paced throughout the sampling period.

    That 15 or 1 second sampling is just happening in the CPU and RAM of the watch, where software could update the display or feed into other fitness or health algorithms. The third level of sampling would be the frequency of logging values into a FIT file that the watch can sync to Garmin Connect later. This is where the 2 minute averaging would occur.

    Because of those averaging windows from sensor to software and from software to log, brief changes in heart rate will be "smoothed out" with the other rates happening during the averaging window. You would have to sustain an elevated rate throughout an entire averaging period in order for it to report the full rate. And, depending on the actual optical sampling rate, there could be "aliasing" where the watch really cannot count the individual beats because some happen in between each time it tries to measure capillary volume in the skin.