The ability to stand up (SU) and sit down (SD) is fundamental for maintaining independence. For individuals using transfemoral passive prostheses, these daily movements place high demand on the intact joints. This demand can be decreased by designing a prosthesis that can support SU and SD. The influence of the ankle on these movements should be understood for this design. This study aimed to determine the effect of ankle angle and range of motion (RoM) on knee joint moments and compensation strategies during SU and SD movements. Fifteen young and able-bodied participants performed SU and SD movements while wearing VariAA boots, a device that can restrict ankle motion. The conditions tested were: an ankle locked in a neutral position, an ankle locked in 15° dorsiflexion, an ankle with a restricted RoM between 0° and 10° dorsiflexion, and an unrestricted ankle. Contrary to the primary hypothesis, the knee joint moments of the unaffected knee did not differ between conditions. However, locking the ankle in a neutral position resulted in several compensatory strategies, such as increased hip joint moment in the affected hip, greater trunk flexion, and increased landing forces during the SD movement. The use of such compensatory strategies has been associated with comorbidities such as osteoarthritis and lower back pain. The findings of this study suggest that even a RoM of 10° can significantly reduce compensatory strategies during SU and SD movements. Incorporating an articulating ankle in prostheses designed to support SU and SD could therefore play a role in mitigating the risk of secondary comorbidities for users of lower
limb prostheses.