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 and walking on uneven ground. Multi-segment foot kinematics was quantified using the Oxford Foot Model, while hip, knee, and ankle kinematics and kinetics were analyzed using the lower-limb Plug-in Gait model 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 showed increased dorsiflexion, while knee and hip flexion increased throughout stance. Kinetically, ankle plantarflexor torque increased during the first half of stance, whereas push-off torque and power were reduced. Concurrently, the knee exhibited increased energy dissipation during push-off, while a tendency toward greater power generation is shown during most of the single-support phase. Overall, these findings highlight a redistribution of joint function and the pivotal role of foot segments kinematics and ankle dynamics in enabling stable locomotion on uneven terrain.