The proposed study aims to characterize the effects of running-specific leg prosthetic stiffness and height during on performance during running and sprinting to optimize running-specific prosthesis prescription. The investigators will collect biomechanical and metabolic data from participants with unilateral and bilateral below the knee amputations while they run at different speeds on a treadmill. This data will be used to understand the effects of running prostheses. Then, these parameters will be used to develop prosthetic prescription techniques for people with below the knee amputations.