Do epoch lengths affect adolescents' compliance with physical activity guidelines?

This study examined the effect of different epoch lengths (from 3 to 60 s) on (a) moderate to vigorous physical activity (MVPA), (b) 10 minutes bouts of MVPA and (c) compliance with World Health Organization (WHO) guidelines, as measured with an ActiGraph accelerometer.

A sample of 401 adolescents (14.48±0.69 years) wore a GT3X accelerometer to measure physical activity (PA) for 7 consecutive days. Data, originally collected in 1-s epoch(s), were then reintegrated into epochs of 3-, 5-, 10-, 15-, 30-, 45- and 60-s.

The results showed a significant epoch effect (P=0.000) for time spent in MVPA, 10-min bouts of MVPA and the extent of compliance with guidelines percentage of compliance of guidelines. Bland-Altman analysis showed good agreement between 5- and 10-, 5- and 15-, and 10- and 15-s data, both for MVPA and 10-min bouts of MVPA.

Epidemiological studies should take into account the sampling interval to offer accurate conclusions with regard to levels of MVPA and the extent to which adolescents comply with guidelines. Shorter epochs, such as 5-, 10- or 15-s are proposed for comparative studies carried out with adolescents in this area.