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

There was a significant three-way interaction between activity, sex, and maturity group for both peak vertical force and average loading rate.

• 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.
• The three-way interaction for PVF was significant: F(4,225)= 4.15, p = 0.003.
• The three-way interaction for ALR was significant: F(4,225)= 5.54, p < 0.001.
• These interactions indicate that the effect of maturity on loading differed across activities and between sexes.

Peak vertical force decreased significantly from Pre- to Post-PHV during walking in both sexes.

• The decrease in PVF from Pre- to Post-PHV during walking was significant in both boys and girls (both p's < 0.001).
• This finding applied to locomotor tasks specifically.
• Linear mixed-effects regression models with fixed effects for activity, sex, maturity group, and their interactions were used.

Peak vertical force decreased significantly from Pre- to Post-PHV during running in boys but not significantly in girls.

• The decrease in PVF during running was significant in boys (p < 0.001).
• Girls showed a similar but non-significant trend during running (p = 0.291).
• Average loading rate also decreased during running in both sexes.

Average loading rate during running decreased with maturation in both sexes, reaching significance in boys and borderline significance in girls.

• ALR decrease during running was significant in boys (p < 0.001).
• The decrease in ALR during running in girls reached borderline significance (p = 0.057).
• ALR was extracted from force-time histories along with peak vertical force.

Boys and girls showed divergent sex-specific patterns in PVF and ALR with maturation during jumping activities.

• Boys tended to maintain or increase PVF and ALR with maturation in the low and high jump activities (p = 0.004–0.914).
• Girls showed consistent reductions in PVF and ALR from Pre- to Post-PHV in jumping activities (p < 0.001–0.057).
• Activities included both low and high jump conditions.
• This divergence suggests girls may receive a reduced osteogenic stimulus from jumping after PHV compared to boys.

Physical activity during childhood is identified as one of the most important modifiable factors influencing osteoporosis risk, yet ground reaction forces associated with typical activities remain largely unknown.

• The influence of sex and maturity on GRFs is rarely considered in existing literature.
• The study aimed to quantify GRF and force loading rates during typical everyday activities including walking, running, jumping, and hopping.
• A portable force plate was used to measure forces across 282 children aged 8-16 years.