Vertical ground reaction forces and loading rates during typical activities in children and adolescents: sex- and maturity-specific considerations for bone health.

Introduction: Despite physical activity (PA) during childhood being one of the most important modifiable factors influencing osteoporosis risk, the ground reaction forces (GRFs) associated with typical physical activities remain largely unknown, and the influence of sex and maturity on these factors is rarely considered. This study aimed to quantify the GRF and force loading rates during typical everyday activities in children and adolescents. Methods: A total of 282 children (127 boys, 142 girls; aged 8-16 years) completed walking, running, jumping and hopping on a portable force plate. Maturity was determined using maturity offset relative to peak height velocity (PHV) and categorised as Pre- or Post-PHV. Peak vertical force (PVF) and average loading rate (ALR) were extracted from force-time histories. Linear mixed-effects regression models were fitted separately for PVF and ALR, including fixed effects for activity, sex, maturity group, their two- and three-way interaction terms, and force-plate type, with participant (ID) as a random effect. Results: There was a significant three-way interaction for both PVF (F Discussion: Findings demonstrate that children and adolescents do not always experience the same osteogenic stimulus for a given activity. Consideration of sex- and maturity-specific loading profiles may therefore be important for designing and interpreting bone-benefitting interventions that deliver an appropriate osteogenic stimulus across childhood and adolescence.