| Daily activities in the form of locomotion require transfer of muscle forces to the environment. Generally, this load transfer was accomplished by the interaction of the foot with the ground. The effectiveness of this process depends on geometric factors such as foot anatomy and placement and functioning of the internal structures of the foot.;The objectives of this work were (i) to explore the possibility to use forefoot anatomy to alter the way the forces were transferred by changing foot placement, (ii) to measure plantar aponeurosis forces to evaluate the amount of Achilles tendon load transmitted to the forefoot, and (iii) to investigate changes in the passive structures of the foot and muscle functioning following surgeries that disturb the integrity of the foot.;Walking initiation experiments were completed with the foot placed internally or externally rotated to meet the first goal. This human subjects study provided changes in the ground reaction force lever arm at the ankle joint, a variable which determines the required muscular moment at the ankle. Effects of partial foot amputation on ankle moment and velocity were also identified in this study by using a computer model of push-off. Cadaver simulations of walking were completed to satisfy the second objective. A fiberoptic measurement system recorded the plantar aponeurosis forces. The sensitivity of this methodology to experiment and calibration conditions were also investigated. Changes in load transfer characteristics after plantar fasciotomy was predicted by a musculoskeletal model. Optimally-controlled muscle excitations simulated a toe-raise task with and without the plantar aponeurosis. Requirements of loading at the arch, redistribution of forces acting underneath the forefoot, and muscle adaptations were quantified.;Foot placement was found to be an effective strategy to change the lever arm of the ground reaction forces. An externally rotated placement, resulted in higher lever arms; simulations of partial foot amputations revealed a decreased muscular demand at the ankle joint with the drawback of increased angular velocity. Temporal loading of the plantar aponeurosis followed a similar pattern of forces applied to the Achilles tendon. The plantar aponeurosis was shown to be a critical component of the load transfer mechanism. Simulations of plantar fasciotomy identified increased torque at the arch, elevated contact forces underneath the metatarsal head and increased activation of the toe flexors, all of which might cause upcoming foot deficiencies. This collection of studies demonstrated the role of forefoot anatomy and plantar aponeurosis on appropriate transfer of muscle forces to the forefoot. |
