Sibship, physical activity, and sedentary behavior: a longitudinal, observational study among Mexican-heritage sibling dyads.

Younger siblings appear to emulate the physical activity behaviors of their older siblings during non-school summer months and sedentary behaviors of older siblings during school-time fall months, especially older brother-younger brother dyads. Family-based interventions to increase physical activity and decrease sedentary behavior are growing in popularity, but more work is needed to understand the role of sibling influences.