Fitbit Zip ionic User Manual page 40

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Note that the heart-rate value appears gray if your watch is searching for a stronger
reading.
Zone Calculation
Below Below
Zone 40% of
your heart
rate
reserve
Fat Burn Between
Zone 40% and
59% of
your heart
rate
reserve
Cardio Between
Zone 60% and
84% of
your heart
rate
reserve
Peak Greater
Zone than 85% of
your heart
rate
reserve
Description
Below the fat burn zone, your
heart beats at a slower pace.
In the fat burn zone, you're likely in
a moderate activity such as a brisk
walk. Your heart rate and
breathing might be elevated, but
you can still carry on a
conversation.
In the cardio zone, you're likely
doing a vigorous activity such as
running or spinning.
In the peak zone, you're likely
doing a short, intense activity that
improves performance and speed,
such as sprinting or high-intensity
interval training.
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