Validity of a brief self-report instrument for assessing compliance with physical activity guidelines amongst adolescents

Objectives: To examine the validity of a brief self-report questionnaire for assessing physical activity, and compliance and non-compliance with moderate-to-vigorous physical activity (MVPA) recommendations in Australian adolescents against accelerometry. Design: Cross-sectional study. Methods: MVPA of 203 adolescents (124 females, 79 males) aged 15-17 years was objectively assessed for 8 consecutive days using uni-axial accelerometers and calculated using age-specific cut-points. Adolescents self-reported the number of days (0-7) they were physically active for a total of at least 60 min/day (1) over the past 7 days and (2) over a typical week. Compliance with physical activity recommendations was defined as (1) 5 and (2) 7 days of self-reported MVPA (of at least 60 min/day), and (3) >= 60 min MVPA per average day, and (4) > 60 min MVPA on every day according to accelerometry. Spearman's Rho correlations analysed the association between accelerometry-derived MVPA/day and self-reported MVPA days/week for the whole sample, sex and weight status. Percent agreement determined the proportion of adolescents correctly identified as not meeting physical activity recommendations (specificity) or as meeting physical activity recommendations (sensitivity) according to the self-report questionnaire. Results: Moderate to large correlations were found between the self-report and accelerometer data (0.2-0.51) across population subgroups. The percent agreement between the self-report and accelerometry data was good for specificity; however, the sensitivity was low, potentially due to poor compliance with recommendations. Conclusions: Compared to accelerometry, the brief MVPA self-report questionnaire appears to have acceptable validity for measuring non-compliance with physical activity recommendations in 15-17 year old adolescents. (C) 2011 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.