Heart Rate Drops After Starting Activity (Race S + HRM-Dual)

[bartolomeo6]

Hi everyone,

I’m experiencing a strange heart rate issue with my Suunto Race S paired with a Garmin HRM-Dual chest strap.

Before starting an activity, the watch seems to receive heart rate data correctly. For example, during my warm-up I can see values above 100 bpm, which matches my effort level.

However, as soon as I start a running activity, the reported heart rate suddenly drops to around 77–81 bpm and stays there for the first 0.5–1 km. Sometimes it takes even longer to recover. Today, during the first 4 km of my run, the watch showed only 116–121 bpm despite running at a steady effort that should have been much higher.

What makes this even more confusing is that after the activity is synced to Strava, the heart rate graph appears to be corrected. Looking at the Strava data, my heart rate was actually around 150 bpm from the beginning of the run, which seems much more realistic.

Has anyone experienced something similar with the Suunto Race S and Garmin HRM-Dual combination? Is this a known issue related to Bluetooth connectivity, chest strap compatibility, or heart rate data processing during activity recording?

Any suggestions would be appreciated.

Thanks!

[matram]

No, but I am using Polar H10.

Have you verified that the Garmin belt is really used, i.e. the green heart icon has a band over it when you start the exercise?

Rarely with my Race S it happens that the optical sensor is used even if I am wearing the belt. In that case HR can look peculiar initially especially if the watch is not snug on the wrist.