Validation of a Single Question for the Evaluation of Physical Activity in Adolescents.

We aimed to assess the validity of a single question to evaluate leisure-time physical activity (PA) in adolescents. We included 209 participants (57.4% girls) aged 14-18 years from Porto, Portugal, evaluated as part of the SALTA project. A self-reported question with four answer options, designed for the EPITeen study, was used to classify the intensity level of usual leisure-time activities. Actigraph accelerometers were used to objectively measure total PA during 7 consecutive days. Since the accelerometers measured PA as a continuous variable, hierarchical cluster analysis was used to identify clusters of individuals with similar level of objectively measured PA. Correlations between self-reported and objective measures were evaluated through polychoric correlations. In girls, we found higher mean time on sedentary activities among those describing their leisure-time PA as "sitting", and an increase on the time spent on light and moderate activities with increasing intensity of PA on self-reported classification. A similar trend was found in boys, but not reaching statistical significance. The correlation between the two measures of PA was 0.42 for girls and 0.46 for boys. We found an acceptable correlation between our single question and the objectively measured PA, showing that, although the single question is not adequate to quantify the intensity of the physical activity, it allows to rank adolescents according to leisure-time physical activity.