Moderate-to-vigorous physical activity among children: discrepancies in accelerometry-based cut-off points.

Objective: To highlight the discrepancies in accelerometry cut-off points of moderate-to-vigorous physical activity (MVPA) according to the definitions of Puyau et al. (MVPA(P)) and Trost et al. (MVPA(T)).

Research Methods And Procedures: Forty-five children from 8 to 11 years old were monitored with the ActiGraph (ActiGraph, LLC, Fort Walton Beach, FL) for 3 consecutive days. Daily time spent at MVPA obtained with MVPA(P) was compared with that obtained with MVPA(T) using variability, regression, and agreement statistics. Data were then discussed with regard to physical activity recommendations.

Results: The mean daily time spent at MVPA(P) (28 +/- 18 minutes) was significantly lower (p < 10(-4)) than that spent at MVPA(T) (141 +/- 39 minutes). The coefficient of determination between the two definitions was low (R(2) = 0.49 +/- 0.71). There was a lack of agreement between the two definitions, with a mean error or bias of 113 min/d. Thirty-four point eight percent and 100% of children underwent 30-minute MVPA/d with MVPA(P) and MVPA(T) definitions, respectively.

Discussion: Comparability between studies devoted to describing children's physical activity or to assessing interventions may lack consistency according to the definition, with a real risk of misclassification.