Physical fitness of primary school children differs depending on their timing of school enrollment. Results from the longitudinal arm of the EMOTIKON-study

Abstract

Abstract Previous research has shown that children who were enrolled according to the legal key date (i.e., keyage children, between eight and nine years in third grade) exhibit a linear physical fitness development in the ninth year of life. In contrast, children who were enrolled with a delay (i.e., older-than-keyage children, OTK, between nine and ten years in third grade) exhibited a lower physical fitness compared to what would be expected for their age. In these cross-sectional studies, age and timing of school enrollment were confounded. In the present longitudinal study, we compared keyage and OTK children at the same age to separately examine effects of timing of school enrollment and age on six physical fitness components: cardiorespiratory endurance (i.e., 6-min run), coordination (i.e., star-run), speed (20-m sprint), power of lower (i.e., powerLOW, standing long jump) and upper (i.e., powerUP, ball-push test) limbs, and static balance (i.e., one-legged-stance test with eyes closed). 1,274 children (i.e., 1,030 keyage and 244 OTK children; 14,516 test scores) from 32 schools were tested in third grade and retested one year later in fourth grade. Both, keyage and OTK children, exhibited a positive longitudinal development in all six fitness components. However, keyage children outperformed age-matched OTK children (both groups on average 9.5 years old) in all six fitness tests. In a post-hoc exploratory analysis, we tested the assumption that some OTK children are biologically younger than indicated by their chronological age. Specifically, one reason for a delayed enrollment could be a child’s perceived biological age at the school-entry exam. In this case, chronological age would correlate negatively with biological age of OTK children. Indeed, a simple reflection of chronological age brought the developmental rate of the chronologically youngest OTK children in line with the one observed for keyage children, but did not eliminate all differences. The mapping of chronological and biological age of OTK children and other possible reasons for lower physical fitness of OTK children remain a task for future research.