Physical activity is associated with a host of positive health outcomes and is shaped by both genetic and environmental factors. We aim to: (1) estimate sibling resemblance in two physical activity phenotypes [total number of steps∙day-1 and minutes for moderate steps per day (min∙day-1)]; and (2) investigate the joint associations of individual characteristics and shared natural environment with intra-pair sibling similarities in each phenotype. We sampled 247 biological siblings from 110 nuclear families, aged 6-17 years, from three Peruvian regions. Physical activity was measured using pedometers and body mass index was calculated. In general, non-significant variations in the intraclass correlation coefficients were found after adjustment for individual characteristics and geographical area for both phenotypes. Further, no significant differences were found between the three sib-ship types. Sister-sister pairs tended to take fewer steps than brother-brother (β = -2908.75 ± 954.31). Older siblings tended to walk fewer steps (β = -81.26 ± 19.83), whereas body mass index was not associated with physical activity. Siblings living at high-altitude and in the Amazon region had higher steps/day (β = 2508.92 ± 737.94; β = 2213.11 ± 776.63, respectively) compared with their peers living at sea-level. In general, we found no influence of sib-types, body mass index, and/or environment on the two physical activity phenotypes.
Keywords: Peru; multilevel modelling; physical activity; shared factors; siblings.