Deformable foot orthoses shift the functional roles of foot and ankle joints during walking gait

Carbon fiber deformable foot orthoses (DFOs) with customizable stiffness may benefit clinical populations by allowing an individual approach to enhancing gait energetics. Prior research suggests that increasing DFO stiffness can decrease energy loss while enhancing energy return at the metatarsophalangeal (MTP) joint, making it more spring-like. However, it remains unclear whether increasing DFO stiffness enhances the mechanics of the midtarsal and ankle joints or only the MTP joint, especially during walking. This study investigated whether walking with increasingly stiff DFOs impacted mechanics or functional roles (damper, motor, spring, strut) of the MTP, midtarsal, and ankle joints. When walking with increased DFO stiffness, the MTP joint showed decreased peak negative power and increased positive work/peak power resulting in more spring- and strut-like behavior. The midtarsal joint had increased peak negative work and decreased positive work resulting in more damper-like and less motor-like behavior. The ankle joint only decreased peak positive power but not work resulting in minimal changes in functional roles. Overall, stiffness-driven energetic gains at the MTP joint were offset by proximal compensations at the midtarsal, suggesting that in healthy gait, DFO-induced energetic benefits may be limited to the MTP joint rather than positively impacting the entire ankle-foot system.