A multilevel analysis of health-related physical fitness. the Portuguese sibling study on growth, fitness, lifestyle and health

Abstract

This study investigates biological, behavioural and sociodemographic correlates of intrapair similarities, and estimates sibling resemblance in health-related physical fitness (PF). The sample comprises 1101 biological siblings (525 females) aged 9-20 years. PF components and markers were: morphological [waist circumference (WC) and %body fat (%BF)], muscular [handgrip strength (GS) and standing long jump (SLJ)], motor [50-yard dash (50YD) and shuttle run (SR)], and cardiorespiratory (1-mile run). Biological maturation was assessed; physical activity (PA), TV viewing and socioeconomic status (SES) information was obtained. On average, older and more mature subjects are better performers in all PF components; PA was negatively associated with SR, while SES was negatively associated with SLJ and SR. A pattern was observed in the intraclass correlations (?) wherein same sex siblings demonstrate greater resemblance for most PF components (sister-sister: 0.35≤ ?≤0.55; brother-brother: (0.25≤?≤0.60) than brother-sister pairs (BS) (0≤?≤0.15), except for %BF (?BB >?SS >?BS), and the 1-mile run (?SS>?BS>?BB). In conclusion, behavioural and sociodemographic correlates play different roles in siblings PF expression. Further, a significant familial PF resemblance was observed with different trends in different sibling types, probably due to variations in shared genetic factors and sociodemographic conditions.