Question

Physical Activity Both mothers' and daughters' physical activity were objectively measured for seven consecutive days, using Actigraph GT3X and GT3X+ accelerometers (ActiGraph, LLC, Fort Walton Beach, FL), which are considered to be valid and reliable for both children [17) and adults [26]. Accelerometers were attached to an elastic belt and worn over the left hip. Monitors recorded 60-s epochs for mothers, and 15-s epochs for daughters [40]. Activity counts were calculated for time spent in moderate (MPA) (4-5.9 METS) and vigorous (VPA) (26 METS) activity. Data with strings of consecutive zeros in bouts of 260 min were deemed non-wear time for mothers, and 20 min [7] for daughters, and retracted from data for analysis. Total counts were divided by total minutes monitored to calcu- late mothers' and daughters' mean count per minute (CPM). Freedson cut-points [20] were applied to the mothers' physical activity data and Evenson cut-points [18] were applied for the daughters [40], to determine the amount of time spent in sedentary and MVPA. To account for the variation in time spent wearing the accelerometers, values were calculated for percentage of monitored time spent in sedentary behavior (% SED), and health-enhancing or moderate-to-vigorous physical activity (% MVPA). Mothers' and daughters' physical activity data were excluded from the analysis if they wore the monitor for £480 min on s4 days [31]. Physical activity mea- surements were calculated for 39 of the 40 mothers, and all 40 of the daughters, after exclusion of participants with insufficient data.

what is the methodology of this physical activity? What do they mean by "epochs" and cut points?

Answer 1

The above case utilises actigraph accelerometer for physical activity measurement. This method is based on measurement of the body's acceleration, that is the change in velocity over time and is expressed in terms of multiples of gravitational force (g).

Epochs is the time sampling interval used to study various physical activity behaviour.

In accelerometer, cut points are definite values used to sort continuous variables into discrete categories.