Question: what does it mean when your heart rate is in the peak zone?
Answer: Fitbit heart rate zones At the top is what Fitbit labels as your Peak Zone, which means your heart rate is above 85% of its maximum. Next below is your Cardio Zone, which covers the ground betwee 70% and 84%, before scaling down to the the Fat Burn Zone when your heart is pumping at between 50% and 69% of its maximum.