Convergent Validity of Pedometer and Accelerometer Estimates of Moderate-to-Vigorous Physical Activity of Youth

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.