Common measures of physical activity (PA) based on duration and intensity do not fully capture its complexity. Adding additional PA-components of muscle strength, mechanical strain, and turning actions, can provide a more complete view of activity behavior.
Based on a prior PhD project, we operationalized PA as five distinct but related components; duration, intensity, muscle strength, mechanical strain, and turning actions. Using longitudinal data, we modeled their long-term trajectories and identified heterogeneous developmental patterns, showing that declines or stability in one component do not automatically mirror changes in others.
The follow-up study integrated these components to examine how these trajectories relate to physical functioning. After all, poor physical functioning limits one ability to remain active, while low levels of physical activity accelerate physical decline, and thus lower physical functioning. Results demonstrated that overall, poor functioning at baseline was indeed associated with the less active trajectories, and that these trajectories were also associated with poor functioning after 10 years follow-up. However, we also found clear differences between components and across sexes in this bi-directional association, advocating for our multidimensional approach.
The final studies advances this work by conceptualizing PA as a dynamic network of interacting components. It will investigates how major life events act as disruptions that may alter the structure and evolution of this network over time. Finally, we will investigate the optimal networks to maintain functioning. Together, this PhD project provides a more nuanced understanding of how activity behavior develops in later life and its relation to healthy aging.