Sibling's resemblance in health- and performance-related fitness among Brazilian youth

Introduction: Physical fitness (PF) is recognized as a crucial element for fostering various health and performance benefits in children and adolescents. Although PF is determined by genetic and environmental factors, little is known about the degree of influence of these factors on PF expression among siblings. Objective: This study aims to examine the degree of sibling resemblance on PF components as well as estimate the influence of individual and contextual factors on sibling resemblance on PF among Brazilian children. Methodology: The sample comprised 784 pairs of siblings (405 boys; 5-15 years), from Lagoa do Carro, Brazil. PF was assessed with the 20-m shuttle run, standing long jump, handgrip strength, shuttle run, 20-m dash, and sit and reach. Anthropometry, biological maturation, gross motor coordination, and school characteristics were also measured. Results: . In general, sibling intraclass correlations differed significantly across sib-ship types for all PF tests. Same-sex siblings (brother-brother or sister-sister) had higher resemblance in the sit and reach, shuttle run, standing long jump, and 20-m dash tests (ρ between 0.06 and 0.36), while opposite-sex pairs (brother-sister) showed higher resemblance in 20-m shuttle run, handgrip, and total PF tests (ρ between 0.05 and 0.27). Further, both individual and school characteristics were associated with the magnitude of sibling resemblance. Conclusions: Our results show significant sibling resemblance in PF traits in Brazilian children. In addition, individual and school characteristics are associated with different PF traits and influence the magnitude of intrapair shared variance, especially for brother-brother siblings.