Minimum Wear Duration for the activPAL Professional Activity Monitor in Adolescent Females.

OBJECTIVES: This study aims to determine the minimum number of days of monitoring required to reliably predict sitting/lying time, standing time, light intensity physical activity (LIPA), moderate-to-vigorous intensity physical activity (MVPA) and steps in adolescent females. METHOD: 195 adolescent females (mean age = 15.7 years; SD = 0.9) participated in the study. Participants wore the activPAL activity monitor for a seven day protocol. The amount of time spent sitting/lying, standing, in LIPA and in MVPA and the number of steps per day were quantified. Spearman-Brown Prophecy formulae were used to predict the number of days of data required to achieve an intraclass correlation coefficient of both 0.7 and 0.8. RESULTS: For the percentage of the waking day spent sitting/lying, standing, in LIPA and in MVPA, a minimum of 9 days of accelerometer recording is required to achieve a reliability of ≥ 0.7, while a minimum of 15 days is required to achieve a reliability of ≥ 0.8. For steps, a minimum of 12 days of recording is required to achieve a reliability of ≥ 0.7, with 21 days to achieve a reliability of ≥ 0.8. CONCLUSION: Future research in adolescent females should collect a minimum of 9 days of accelerometer data to reliably estimate sitting/lying time, standing time, LIPA and MVPA, while 12 days is required to reliably estimate steps.

Comparison of accelerometry cut points for physical activity and sedentary behavior in preschool children: a validation study.

This study compared accelerometry cut points for sedentary behavior, light and moderate to vigorous intensity activity (MVPA) against a criterion measure, the Children's Activity Rating Scale (CARS), in preschool children. Actigraph accelerometry data were collected from 31 children (4.4 ± 0.8 yrs) during one hour of free-play. Video data were coded using the CARS. Cut points by Pate et al., van Cauwenberghe et al., Sirard et al. and Puyau et al. were applied to calculate time spent in sedentary, light and MVPA. Repeated-measures ANOVA and paired t tests tested differences between the cut points and the CARS. Bland and Altman plots tested agreement between the cut points and the CARS. No significant difference was found between the CARS and the Puyau et al. cut points for sedentary, light and MVPA or between the CARS and the Sirard et al. cut point for MVPA. The present study suggests that the Sirard et al. and Puyau et al. cut points provide accurate group-level estimates of MVPA in preschool children.

Comparison of epoch and uniaxial versus triaxial accelerometers in the measurement of physical activity in preschool children: a validation study.

The objectives of this study were to explore whether triaxial is more accurate than uniaxial accelerometry and whether shorter sampling periods (epochs) are more accurate than longer epochs. Physical activity data from uniaxial and triaxial (RT3) devices were collected in 1-s epochs from 31 preschool children (15 males, 16 females, 4.4 ± 0.8 yrs) who were videoed while they engaged in 1-hr of free-play. Video data were coded using the Children's Activity Rating Scale (CARS). A significant difference (p < .001) in the number of minutes classified as moderate to vigorous physical activity (MVPA) was found between the RT3 and the CARS (p < .002) using the cut point of relaxed walk. No significant difference was found between the GT1M and the CARS or between the RT3 and the CARS using the cut point for light jog. Shorter epochs resulted in significantly greater overestimation of MVPA, with the bias increasing from 0.7 mins at 15-s to 3.2 mins at 60-s epochs for the GT1M and 0 mins to 1.7 mins for the RT3. Results suggest that there was no advantage of a triaxial accelerometer over a uniaxial model. Shorter epochs result in significantly higher number of minutes of MVPA with smaller bias relative to direct observation.