Background: Dynamic stiffness can be used for studying foot pathologic abnormalities and for developing prostheses and orthoses. Although previous works have studied the role of ankle joint stiffness during gait, other foot joints have not yet been analyzed. We sought to characterize the dynamic stiffness of the ankle, midtarsal, and metatarsophalangeal joints during normal walking.

Methods: Kinematics and contact data from four healthy individuals during walking were registered with a three-dimensional motion analysis system and a pressure platform. Stance phases with flexion moment-angle linear relationships were identified, and dynamic stiffnesses were calculated from the slope of their linear regressions. Intraparticipant repeatability was analyzed using analyses of variance, and interparticipant variability was checked through the SD of averaged participant stiffnesses.

Results: Flexion moment-angle linear relationships were identified (R2 > 0.98) during the early and late midstance phases and the propulsion phase at the ankle (2.76, 5.23, and 3.42 N·m/kg/rad, respectively) and midtarsal (15.88, 3.90, and 4.64 N·m/kg/rad, respectively) joints. At the metatarsophalangeal joint, a linear relationship (R2 > 0.96) occurred only during the propulsion phase (0.11 N·m/kg/rad). High dynamic stiffness variability was observed during the late and early midstance phases at the ankle and midtarsal joints, respectively.

Conclusions: These results may serve as a basis for future studies aimed at investigating the role of dynamic stiffness identified herein in different foot disorders. The importance of properly controlling the samples in such studies is highlighted. Study of the dynamic stiffnesses identified might be used in the design of prostheses, orthoses, and other assistive devices.

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