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Forerunner 645 - Heartrate Values

Former Member over 4 years ago

Hi everybody,

with the Forerunner 645 optical sensor the heartrate measurements were always more or less accurate when in rest or with no major activity. So were measuring values when riding a bike (road or mountain). But the values are comletely out of range while running. My max. heartrate is about 165. I'm getting values up to 180 during normal running. Values should then be around 130. I always keep the sensor clean, my wrist is shaved and I'm wearing the 645 at the recommended position on the arm. It seems that the problem gets worse over time.

Anybody with a similar experience? Is there a fix?

Looking forward to your kind feedback - Axel

0 dom over 4 years ago

Try wearing a chest strap and see what values you get.

0 DaKo over 4 years ago

Yes, try a comparison with a chest strap. Only then you can tell if your garmin heartrate is too high. Mine is quiet accurate while running. Not spot on, but surely not a difference>5.

0 Piero over 4 years ago

the same thing happens to me if I wear it too large

0 Former Member over 4 years ago in reply to DaKo

Hi, thanks for responding. Before I changed to Garmin about a couple of years ago, I used a Polar V800 with a chest strap. From that time I know exactly my heartrate range. And I can tell the current values measured with the FR 645 optical sensors are more than 15 up to 30 beats wrong.

Today I ran a longer distance at a more comfortable speed. Result is that the deviation is not that large as with higher intensity runs. Maybe the impact of the feet when contacting the ground plays a role.

There is a pattern which is obvious from the heartrate diagram of a run or bike ride and indicates a faulty measurement. There are step-like sudden increases or decreases of the heartrate in the order of more than 10 beats per minute. And this is not normal.

I'll start to change the way to wear the FR 645 and see what happens. Let you know the result. Keep healthy - Axel

0 Garmin-Brooks over 4 years ago in reply to Former Member

You might be running into this:

False Heart Rate Detection

Changes in blood volume aren't always caused by changes in heart rate. Your vascular system is like a balloon, so the movement of your body or flexing of large muscle groups can affect the level of blood volume in the wrist area and make it more challenging to accurately detect heart rate among the presence of other signals that have a much larger magnitude and that change more dynamically.

In the following example, the watch initially detected and locked onto the runner's pulse, but around 20 minutes in it locked to their running cadence:

Try confirming that the watch has calibrated heart rate prior to starting. There are a couple of ways to check. First, if your run profile is the only favorite activity you'll see Run, and then a track shaped oval with a battery icon and a flashing heart. If you take off prior to that heart turning solid it won't be completely calibrated. If you have more than one favorite activity, go to the screen that shows your data fields, a black banner will take up the top third of the screen, with a battery icon and a flashing heart rate icon. You can observe heart rate calibration from there as well.