THE EFFECT OF ACCELEROMETER EPOCH ON PHYSICAL ACTIVITY OUTPUT MEASURES

Accelerometers are used to assess the total activity and time spent at varying intensities of activity. The timesampling interval (epoch) used in most field studies is 60 s, as use of epochs lower than this result in limited recording time. The short-burst nature of children’s activity can lead to inaccuracies when using long epochs. The purpose of this study was to evaluate the influence of accelerometer epoch on activity measures. Twenty-five 7–11-year-old children (height133.17.1 cm, body mass32.06.8 kg) wore two RT3 accelerometers for 6 h. Activity was recorded at 60-s and 1-s epochs. Output measures were total activity and minutes spent in light (3 metabolic equivalents, METs), moderate (3–6 METs), vigorous (6–9 METs), hard (9–12 METs), and very hard (12 METs) intensity activities. Relative to the 1-s epoch, the 60-s epoch overestimated the time in moderate activity (60-s epoch40.017.1 min, 1-s epoch30.66.7 min) and vigorous activity (60-s epoch11.6 0.9 min, 1-s epoch8.40.4 min), but underestimated the time in very hard activity (60-s epoch3.70.9 min, 1-s epoch12.41.0 min). Total activity and time recorded in light and hard activity did not differ by epoch setting. In conclusion, a 1-s epoch is recommended when assessing vigorous activity. This is particularly important when assessing the relationship between bone health and activity as bone mass is increased by short periods of intense activity.