Early Motor Development and Physical Activity: A Behavioral Genetic Approach

This dissertation, “Early Motor Development and Physical Activity: A behavioural Genetic Approach,” focuses on the familial confounders between motor development and physical activity during childhood and early adolescence, to find out the potential modifiable determinant of physical activity. The research is grounded in the theoretical framework of the Stodden model, which suggests a direct causation between motor competence and future physical activity. By utilizing data from the Netherlands Twin Register (NTR), this dissertation explores how genetic and environmental factors contribute to individual differences in motor development and exercise behavior across childhood and early adolescence. The research begins by examining early motor development, including motor milestones before age 2 years (e.g., rolling over, sitting without support, crawling, standing unaided, walking independently) and gross motor skills at age 5 (e.g., throwing, kicking, and catching a ball, and hopping, one-leg standing, walking down the staircase), and how these motor competence can predict later physical activity levels in childhood and adolescence. Chapter 1 introduces the foundational concepts of motor competence and physical activity, and the methodological twin design to quantify the familial effects on motor competence and physical activity. While Chapter 2 and Chapter 3 focus on the genetic underpinnings of physical activity and sedentary behavior, highlighting the limited understanding of molecular genetic findings in children’s exercise ability. The dissertation also addresses the confounding effects of familial factors, such as shared environments and genetics, in the relationship between motor competence and physical activity. Chapters 4 and 5 dive deeper into the genetic and environmental influences on motor milestone achievements and the correlation between early motor competence and later physical activity. The findings reveal that early motor competence explains a modest portion of the variance in physical activity, with a notable genetic influence. Specifically, the results suggest that in boys, the relationship between early motor development and later exercise behavior is largely driven by shared genetic factors. However, in girls, this relationship appears weaker, with no clear evidence of a causal connection between motor competence and physical activity. Finally, Chapter 6 provides a critical review of the Stodden model by synthesizing findings from various reviews and addressing gaps in the understanding of the model's causal pathways. The study concludes that while early motor competence is associated with physical activity, the evidence for a strong causal link is limited. Familial factors, including genetics and shared environment, play a substantial role in the relationship, casting doubt on the straightforward causality proposed by the Stodden model. The dissertation calls for further research using genetically informed methods to better understand the developmental trajectories of motor competence and physical activity.