Foot Segments Motion during Uneven Terrain Walking and Influence on Lower Limb Biomechanics

Human locomotion has been extensively studied on flat ground; however, everyday walking often occurs on uneven terrain, which poses additional biomechanical challenges. The role of foot segmental mobility under these conditions remains underexplored. This study investigated how irregular surfaces influence foot kinematics and lower-limb biomechanics. Twelve able-bodied young adults performed eight barefoot tasks at self-selected speed, including level walking, obstacle crossing, walking on uneven ground, ramp, and stairs. Kinematic data were collected using the multi-segment Oxford Foot Model, and hip, knee, and ankle biomechanics were analyzed to identify compensatory strategies. Participants exhibited increased plantarflexion of the hallux and forefoot, increased dorsiflexion of the forefoot and hindfoot relative to the tibia, and a reduced range of motion of the foot segments, suggesting a stiffening strategy to enhance grip and stability. Ankle range of motion decreased, while knee and hip flexion slightly increased throughout stance. Kinetically, ankle plantarflexor torque increased during the first half of stance, whereas push-off torque and power were reduced. Concurrently, negative power absorption at the knee increased, confirming its role as a mechanical damper. Overall, these findings highlight a redistribution of joint function and the pivotal role of foot segments and ankle dynamics in enabling stable locomotion on uneven terrain.