Most physical activity (PA) questionnaires assess moderate to vigorous PA (MVPA) describing the physical exertion of individuals that might be influenced by their physical fitness. Therefore, the aim of this study was to determine whether fitter children could better assess their PA with the questionnaire than less fit children. The cross-sectional validation study was conducted with 108 children (60 girls) aged 11 to 14 years, who were divided into three fitness groups based on the results of the 600 m running test. To answer the research question, the agreement between their assessment of PA using the SHAPES questionnaire and the UKK RM42 accelerometer data was analysed. One quarter of the participants achieved at least 60 min of MVPA each day, measured by accelerometer. The average MVPA obtained was 97.8 ± 35.6 min per day, with the high fitness group having a significantly higher value compared with the other groups. Moderate to high validity coefficients were found in the high fitness group (Spearman's ρ range 0.34-0.70). In contrast, the lower fitness groups had poor to moderate validity for all variables (Spearman's ρ range 0.03-0.42). These results suggest that the fittest children self-assess their PA with the questionnaire better than less fit children, which may advance new directions for the development and evaluation of PA questionnaires and their usability.
Keywords: accelerometer; assessment; physical fitness; reliability; validity; youth.