This device is used to test below knee, or “transtibial”, prostheses. These are beneficial because recruiting subjects for intermediate trials or troubleshooting can be a major setback in terms of development time. Currently, researchers are attaching prostheses to the underside of an aircast boot. This setup requires a lift shoe on the contralateral side and a brave subject. Additionally, the gait of the subject is irregular due to an extended shank and foot. The device proposed retains the rotational component of the knee and control for mass of the researchers shank by spring. Since the anthropometry more closely matches the ideal, a lift shoe isn’t needed.