Although a number of above-knee amputees have expressed a desire to participate in recreational activities involving running, no currently available lower limb prosthesis has proven adequate in allowing amputees to achieve a natural, efficient, one-to-one running gait. Until recently, amputee runners such as Terry Fox and Steve Fonyo have adopted a variety of asymmetrical gaits, although the Terry Fox Jogging Prosthesis has allowed some amputees to achieve an inefficient one-to-one running pattern. The objective is to design a conservative running prosthesis which will functionally imitate the intact limb during running activities. The prosthesis performance criteria were established for both stance and swing, based on an examination of non-amputee running biomechanics. The prosthesis incorporates a shank unit assembly which linearly compresses upon heel-strike, absorbing the impact energies in a helical coil compression spring, and then uses a ratchet device to store these impact energies throughout the stance phase. In late stance, the natural dorsi flexion of the prosthetic foot initiates the release of the stored energies, propelling the amputee upward and forward into the swing phase. It is recommended that a comprehensive biomechanical gait analysis be performed on the prosthesis' operation to allow for optimization of its configuration and performance. In conclusion, the features of this prosthesis will allow above-knee amputees to achieve a more natural, one-to-one running gait and participate more actively in activities involving running. / Thesis / Master of Engineering (ME)