Moderate and vigorous physical activity (MVPA)

MVPA is calculated from the intraday data file we collect from Fitbit. The formula we are using to calculate MVPA is the total number of minutes that a participant had greater than or equal to 100 steps. This formula is consistent across all studies on Way to Health that are collecting intraday pedometer data from Fitbit.

A participant would have a value of 0 for their daily MVPA if they did not walk over 100 steps during any given minute of that day.

Sedentary minutes, lightly active minutes, fairly active minutes, and very active minutes are pulled directly from the Fitbit. Fitbit calculates these as:

“Fitbit devices use data from two sensors to compute various measures of activity: a 3-axis accelerometer and a heart rate sensor.  From the accelerometer data, Fitbit computes daily counts of steps and floors climbed.  It also calculates for every non-sleeping minute of the day whether a person is in one of four states based on the accelerometer reading:  sedentary, lightly active, fairly active and very active.  Fitbit aggregates this data to compute daily minutes in each of these activity zones.  

From the heart rate sensor data, Fitbit calculates for every non-sleeping minute whether a person is in one of four categories: low range, fat burn, cardio, or peak.  Fitbit aggregates this data to compute daily minutes in each of these heart rate zones.”