This article presents the modelling principles of the joint constraints for flexible multibody systems. The joints are composed using three basic constraint primitives which are derived including their first and second time derivatives as well as the components of the Jacobian matrix. The description of the derived components of constraint primitives can be used to develop a library of kinematic joints to use in multibody codes. In this study, the equations of motion are defined using generalized Newton-Euler equations where the deformations are accounted for by using the floating frame of reference formulation with modal coordinates. The deformation modes used in the floating frame of reference formulation are obtained from the finite-element analysis by employing the lumped mass matrix. Dynamic analysis of a mechanism consisting of rigid and flexible bodies is used to illustrate the validity of the constraint formulation.

Individuals at risk of Developmental Coordination Disorder (DCD) have low levels of physical activity in childhood due to impaired motor competence; however, physical activity levels in adulthood have not been established. This study sought to determine the impact of DCD risk on physical activity levels in adults using accelerometry measurement. Participants (n = 656) from the Arvo Ylppö Longitudinal Study cohort had their motor competence assessed at the age of five years, and their physical activity quantified via device assessment at the age of 25 years. Between group differences were assessed to differentiate physical activity measures for individuals based on DCD risk status, with general linear modeling performed to control for the effects of sex, body mass index (BMI), and maternal education. Participants at risk of DCD were found to have a lower total number of steps (d = 0.3, p = 0.022) than those not at risk. Statistical modeling indicated that DCD risk status increased time spent in sedentary light activity (β = 0.1, 95% CI 0.02 to 0.3, p = 0.026) and decreased time spent in vigorous physical activity via interaction with BMI (β = 0.04, 95% CI 0.001 to 0.1, p = 0.025). Sensitivity analysis found that visuomotor impairment did not significantly impact physical activity but did increase the role of DCD risk status in some models. This 20‐year‐longitudinal study indicated that DCD risk status continues to negatively impact on levels of physical activity into early adulthood.