Epoch length and the physical activity bout analysis: An accelerometry research issue

One hundred thirty-four adults (50？±？7？years) wore an accelerometer (Lifecorder) for 7 consecutive days under free-living conditions in order to determine the time spent in physical activity of light intensity (LPA), moderate intensity (MPA), vigorous intensity (VPA), moderate to vigorous intensity (MVPA), and the total physical activity (TPA; sum of LPA, MPA and VPA). Additionally, all PA was divided according to the bout durations (sporadic, >3？min, >5？min, and？>？10？min). These indices of PA were analyzed using three different epoch lengths (4？sec, 20？sec and 60？sec) derived from the accelerometer.The LPA significantly increased in association with increases in the epoch length (48.7？±？15.9 to 178.7？±？62.6？min/day, p？<？0.05). The amount of sporadic VPA determined by the shortest epoch length (2.9？±？5.2？min/day) was significantly longer than the two remaining epoch lengths (1.1？±？2.4 to 0.9？±？2.5？min/day, p？<？0.05). The times of the MVPA bouts lasting longer than 3？minutes determined using the 4-second epoch length (2.6？±？5.4 to 7.7？±？10.0？min/day) were significantly shorter than those determined using the other two settings (6.5？±？10.5 to 13.8？±？13.8？min/day, p？<？0.05). The frequencies of the MVPA bouts lasting longer than 10？minutes determined using the 4-second epoch length (0.2？±？0.3 bouts/day) were significantly lower than those determined using the other two settings (0.3？±？0.4 bouts/day, p？<？0.05).The epoch length setting of the accelerometer affects the estimation of the PA bouts under free-living conditions in middle-aged to older adults.The American College of Sports Medicine and the American Heart Association recommend that all healthy adults 18 to 65？years of age engage in moderate-intensity aerobic (endurance) physical activity (MPA) or vigorous-intensity aerobic physical activity (VPA) in order to promote and maintain health [1]. Since several consensus statements also recommend engaging in moderate to vigorous intensity physical activity (MVPA) [2,3]