BPM for different Zone

[Zeff]

My moderate/vigorous range always keep changing which is fine. I would like to know if moderate range 111 to 138 is better or 115 to 139 is better in terms of cardiovascular perspective?

[Triletics]

Insignificant. There are different models for HR zones (Fitbit uses the most simplified) but the body response to changing HR is a lot more fluid (your heart doesn't know that it's beating in 'moderate' or 'vigorous'). Zones should be used as descriptive not prescriptive. It means that absolute numbers don't mean as much as keeping your effort (RPE) at the right (described by a particular zone) level. Whether it's 139 or 138 - no difference, no meaning.

[LZeeW]

Hello @Zeff and welcome to the Community.  I want to add some additional information that will help explain why Fitbit reports data this way.  Fitbit is a US company and uses both CDC and American Heart Association (AHA) recommendations for activity.  Both recommend a minimum of 150 minutes/wk of moderate activity or 75 minutes/wk of vigorous activity or a combination of the two.  This is why vigorous/peak minutes are 2x moderate minutes.  This is also why your Fitbit is set with a default goal of 150 zone minutes per week.

Fitbit's heart rate zones use your resting heart rate as part of the calculation.  Your zones will change if your resting heart rate changes.

Yes, Fitbit's zones are simplified compared to the five heart rate training zones.  But it is designed for a specific purpose.