Validity and Reliability of the 'Feelfit®' Accelerometer in Evaluating Physical Activity and Sedentary Time in Children: A Comparative Study with Two Different Accelerometers.

Accurate physical activity (PA) measurement is crucial for public health surveillance. While self-report questionnaires are commonly used, they have limitations, especially in young children. An affordable and user-friendly device like Feelfit® offers a promising alternative particularly for countries with limited research resources. This study aimed to evaluate Feelfit®'s performance against the widely used ActiGraph® accelerometer in measuring PA among children. A quasi-experimental design was applied. Thirty-nine children (19 boys; 20 girls; aged 11.4 ± 0.5 years) wore both Feelfit® and ActiGraph® during sequentially specified activities of varying intensity ranging from sedentary to vigorous. Data were analysed using paired t-tests, Bland-Altman plots, and intra-class correlation coefficients (ICCs) to assess agreement, precision, and reliability. Feelfit® showed good agreement with ActiGraph® for moderate-to-vigorous PA (MVPA) but overestimated sedentary time and underestimated light PA. It demonstrated better precision for MVPA but low reliability for light PA. Intra-class correlation coefficients were moderate for MVPA (ICC = 0.43), but poor for sedentary time (ICC = 0.11). Feelfit® is a suitable option for measuring MVPA in children, offering acceptable validity and reliability compared to ActiGraph®. However, improvements are needed for accurate measure of sedentary and light activities. Despite these limitations, Feelfit®'s affordability and ease of use make it a valuable tool for use in small- to large-scale research and in resource-limited settings.