Can Pedometers Estimate Moderate-to-Vigorous Physical Activity of Youth? Comparison with Accelerometry

Abstract

Given the current economic climate, the costs associated with assessing free-living physical activity (accelerometers $335/unit - ActiGraph), and issues regarding unit loss/damage during assessments, researchers need a low-cost and accurate assessment of moderate-to-vigorous intensity physical activity (MVPA). If a pedometer can provide estimates of MVPA that are comparable to accelerometry-derived MVPA, this would have a profound impact on researchers, practitioners, and the general public. Pedometer step frequency thresholds (120 steps·min-1, SPM) that correspond to MVPA have been proposed for youth. Pedometers now have internal mechanisms to record time (hrs:min:sec) spent at or above a user-specified SPM threshold. PURPOSE: The purpose of this study was to compare pedometer estimates of MVPA based on 120 SPM to accelerometer-derived MVPA from 5 cutpoints established for youth. METHODS: One-hundred and forty-nine youth (age 8.6yrs±1.7, 60 girls) attending summer camp wore an Actigraph accelerometer (5 second epochs) and a Walk4Life MVPA pedometer (120 SPM) for an average of 5.7 hours·day-1 ±0.8hrs. Five accelerometer cutpoints were used to compare pedometer MVPA estimates (P-MVPA): Treuth (TR), Mattocks (MT), Evenson (EV), Puyau (PU), and Freedson child equation (FR). Bland-Altman plots, paired t-tests, and regression analyses were used to compare MVPA estimates between devices. RESULTS: Overall, P-MVPA was 24.6min±16.7 vs. TR 25.2min±16.2, MT 18.8min±13.3, EV 36.9min ±21.0, PU 22.7min±15.1, and FR 50.4min±25.5. Paired t-tests indicated significant differences between P-MVPA and MVPA estimated from EV (t = 9.16, P <.01), MT (t = 5.33, P <.01), and FR (t = 16.43, P <.01). No significant differences were observed for PU (t = 1.76, P =.08) and TR (t = 0.51, P =.61). More active youth and those classified as obese (≥95th percentile) exhibited a larger discrepancy between pedometer and accelerometer MVPA estimates. CONCLUSIONS: Pedometer-determined MVPA provided comparable estimates to accelerometer-determined MVPA for two (TR, PU) of the 5 comparisons. Obesity and activity level had a significant effect on the difference between devices. Nevertheless, these findings provide preliminary evidence supporting the use of pedometers to estimate youth MVPA.