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Cheryl L. Addy, Jennifer L. Trilk, Marsha Dowda, Won Byun and Russell R. Pate

The purpose of this study was to determine the minimum number of days of accelerometry required to estimate accurately MVPA and total PA in 3- to 5-year-old children. The study examined these metrics for all days, weekdays, and in-school activities. Study participants were 204 children attending 22 preschools who wore accelerometers for at least 6 hr per day for up to 12 days during most waking hours. The primary analysis considered the intraclass correlation coefficient (ICC) for each metric to estimate the number of days required to attain a specified reliability. The ICC estimates are 0.81 for MVPA-all days, 0.78 for total PA-all days, 0.83 for MVPA weekdays, 0.80 for total PA-weekdays, 0.81 for in-school MVPA, and 0.84 for in-school total PA. We recommend a full seven days of measurement whenever possible, but researchers can achieve acceptable reliability with fewer days, as indicated by the Spearman-Brown prophecy: 3–4 days for any weekday measure and 5–6 days for the all-days measures.

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Michael William Beets, Charles F. Morgan, Jorge A. Banda, Daniel Bornstein, Won Byun, Jonathan Mitchell, Lance Munselle, Laura Rooney, Aaron Beighle and Heather Erwin

Background:

Pedometer step-frequency thresholds (120 steps·min-1, SPM) corresponding to moderate-to-vigorous intensity physical activity (MVPA) have been proposed for youth. Pedometers now have internal mechanisms to record time spent at or above a user-specified SPM. If pedometers provide comparable MVPA (P-MVPA) estimates to those from accelerometry, this would have broad application for research and the general public. The purpose of this study was to examine the convergent validity of P-MVPA to accelerometer-MVPA for youth.

Methods:

Youth (N = 149, average 8.6 years, range 5 to 14 years, 60 girls) wore an accelerometer (5-sec epochs) and a pedometer for an average of 5.7 ± 0.8 hours·day-1. The following accelerometer cutpoints were used to compare P-MVPA: Treuth (TR), Mattocks (MT), Evenson (EV), Puyau (PU), and Freedson (FR) child equation. Comparisons between MVPA estimates were performed using Bland-Altman plots and paired t tests.

Results:

Overall, P-MVPA was 24.6 min ± 16.7 vs. TR 25.2 min ± 16.2, MT 18.8 min ± 13.3, EV 36.9 min ± 21.0, PU 22.7 min ± 15.1, and FR 50.4 min ± 25.5. Age-specific comparisons indicated for 10 to 14 year-olds MT, PU, and TR were not significantly different from P-MVPA; for the younger children (5−8 year- olds) P-MVPA consistently underestimated MVPA.

Conclusions:

Pedometer-determined MVPA provided comparable estimates of MVPA for older children (10−14 year-olds). Additional work is required to establish age appropriate SPM thresholds for younger children.