Biomechanical effects of asymmetric backpack shoulder straps on the unilateral flatfoot: a finite element analysis

This study investigated the biomechanical effects of asymmetric backpack shoulder strap configurations on individuals with unilateral flatfoot (UF) using finite element analysis (FEA). A male subject with UF was recruited, and different shoulder strap settings were simulated to assess their impact on plantar fascia and Achilles tendon stress and strain, as well as on changes in foot arch morphology. The results showed that using equal-length straps on both shoulders resulted in lower stress and strain levels in the plantar fascia and Achilles tendon during walking. However, when the strap length on the flatfoot side was increased, the longitudinal and transverse arch deformation of the affected foot also increased, while deformation in the normal foot's longitudinal arch was reduced. These findings suggest that lengthening the strap on the flatfoot side may help improve arch morphology on that side, but at the cost of increased soft tissue loading and potential restriction of normal foot development.