The biomechanics of the human foot
This thesis reports on work undertaken to study the biomechanics of the human foot during normal daily activity, particularly walking and standing. A literature review is presented on topics related to the subject and several of the areas demanding further investigation are highlighted. Three lines of enquiry were pursued to consider the kinematics, kinetics, passive structural properties and muscle activity associated with the foot. A dynamic pedobarograph with a synchronised video system was used to measure the forces and their distribution under the foot (based on seven marked areas) and six kinematic angles of the foot and lower leg. Sixty-one healthy subjects were assessed and the results are presented. Kinetic and kinematic parameters were found to be consistent and smooth for the test population. Several of the events of the gait cycle were found to be temporally different from values widely reported. In the second investigation, four cadaveric foot specimens were tested dynamically to determine the role of the plantar structures during loading in various positions. A method of sequential dissection was used and the results support many of the theories regarding ligament function. Tests on the effect of three extrinsic muscles on the foot load distribution also support previous studies while a preliminary investigation of two pathological feet partially clarifies the biomechanical effects of a hallux valgus deformity. Eight of the foot extrinsic and intrinsic muscles were assessed for the final investigation. Using electromyographic (EMG) recording techniques on six healthy subjects, the muscle EMG activity was quantified during walking a) barefoot, b) with a moulded heel plate, and c) with soft shoes. The results for the extrinsic muscles generally agree with previous work, while the intrinsic muscle activity is more variable. The intrinsic muscles were more active when shoes were worn and displayed unusual fatigue patterns.