Which exercise mode do I use on Charge 6?

[ninaoostv24]

I want to track my exercise when doing circuit training/HIIT at my gym. Which exercise mode should I select? HIIT, Circuit training, Strength training?  What is the Fitbit actually doing in these modes?

Moderator Edit: Clarified subject

[SunsetRunner]

I am not syncing Fitbit with Strava, but something similar is happening to me as well when I am syncing my runs from Polar Flow to Strava. Like the average heart beat would be different or average pace. It might be that Strava is applying its own calculations when transfering data over. Just a guess. Like today, on Polar Flow the pace was 9:12 min/km, on Strava 9:10 min/km, HR avg 128 bpm compared to 129 bpm on Strava. Not much of a difference but still. It shows that Strava does not simply copy the data over.

[Triletics]

@ninaoostv24 when you upload to Strava, the GPS distance is calculated and you see "moving time" as a duration (Fitbit shows elapsed time). Pace is recalculated based on moving time and GPS distance. Charge 6 doesn't use GPS to estimate distance during run hence differences (actual map distance is always different than distance reported by Fitbit). Strava integration is quite poor.

@SunsetRunner that is correct that Strava recalculates the data however there is a way to prevent it and force Strava to get data "as-is" which is done so by Garmin or Suunto.