Direction of Change in Cardiorespiratory Fitness in School-Age Children: A Longitudinal Single-Centre Study

<b>Background/Objectives</b>: Cardiorespiratory fitness (CRF) is currently a topic of widespread interest in the field of public health, considered as the basic marker for health status assessment. Better CRF is generally accepted to be beneficial in cardiovascular and metabolic disease prevention, both in children and in adults. The aim of this study was to present the direction of change in the cardiorespiratory fitness of Polish children aged 9 to 13 in a longitudinal study. <b>Methods</b>: Three series of cardiorespiratory fitness measurements were performed on school-aged children at one-year intervals. CRF was assessed based on the number of laps run in the 20 m shuttle run test (20mSRT). In order to check the level of cardiorespiratory fitness in consecutive years, the 20mSRT results were compared to the international percentile norms, considering the children's sex and age. <b>Results</b>: The number of completed laps shows great diversity with reference to age. Together with age, the advantage of boys in terms of the number of completed laps becomes visible. The distribution of percentile classification results in subsequent tests across the whole study population shows that a low percentage of children who were qualified for the study had their CRF below the 20th percentile, and a relatively high percentage was above the 80th percentile. <b>Conclusions</b>: For the whole test group, the results of the percentile classification did not change significantly in subsequent tests. It is worth noting, though, that together with age, CRF changes evolved towards higher values in the tested group, as a vast majority was at the level of the 50th percentile. However, still a significant group of the tested children remained within the low percentile values of CRF.