Cross-sectional associations between accelerometry-measured physical activity and physical fitness among elementary...

Physical activity (PA) is essential for children's physical and mental health, with moderate-to-vigorous physical activity (MVPA) playing a key role in improving physical fitness (PF). Despite its benefits, PA levels among children are insufficient, and PF levels have declined, highlighting the need for targeted interventions. PA was measured using accelerometers and expressed as total PA (counts per minute (cpm) and MVPA (min·day^-1). PF was measured using the Test of Physical Fitness (TPF). The primary objective was to examine (a) the association between device-measured PA and PF in school-aged children (6-12 years), b) to explore the extent to which this association can inform the amount of PA needed to influence TPF scores, and (c) whether sex, age, or body mass index (BMI) modifies the association between PA and PF. A sample of 216 school children aged 6, 8, 10 and 12 years from Northern Norway participated. Multivariable linear regression analyses were conducted, adjusting for sex, age, BMI, wear time, and school. In multiple adjusted analyses, we observed an association between children's PA level and TPF. MVPA was positively associated with PF in the overall population and across sex, age, and BMI subgroups, whereas the association of total PA with PF was significant only for boys and girls, older children, and normal weight children. These findings emphasize the importance of promoting PA, especially MVPA, to enhance PF in children, with tailored approaches for younger, overweight, and less active children.