Objectives: The physical activity (PA) levels of Spanish adolescents must be determined to assess how the lack of PA may affect the increasing prevalence of obesity. Thus, to assess PA in this age range valid measurement instruments are essential. The aim of this study was to evaluate the validity of four easily applied questionnaires (the enKid and FITNESSGRAM questions, the Patient-Centered Assessment and Counselling [PACE] questionnaire, and an activity rating) to assess PA in Spanish adolescents by using an accelerometer as the criterion instrument. Methods: A total of 232 adolescents (113 girls) completed the questionnaires and wore an ActiGraph accelerometer for 7 consecutive days. Spearman's correlation coefficient (rho) was used to compare the questionnaires and total PA, moderate PA, vigorous PA and moderate-to-vigorous PA (MVPA) assessed by the accelerometer. Results: All the questionnaires showed moderate correlations when compared against total PA (rho=0.36-0.43) and MVPA (rho=0.34-0.46) obtained by the accelerometer in the total sample. Higher correlations were found when comparing the questionnaires against vigorous PA (rho=0.42-0.51) than against moderate PA (rho=0.15-0.17). The FITNESSGRAM question and the PACE questionnaire obtained weak correlations in girls and the enKid question and activity rating were moderately correlated for boys and girls. Conclusions: The four questionnaires evaluated showed acceptable validity in the assessment of PA in the Spanish adolescent population. © 2008 SESPAS.

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