Introduction: Paresis in UMND patients leads to immobilization and disuse of the ankle joint. As a result, secondary changes such as increased passive stiffness and plastic CNS rearrangements aggravate the paresis. We propose an intervention that compensates the passive stiffness, enabling the remaining muscle force to initialize movement to prevent immobilization and disuse and to maximize controllability. Passive stiffness compensation is achieved by applying negative stiffness. The research question is: Does negative stiffness increase active RoM and how does this effect controllability of the ankle joint. Methods: By applying, subject speci?c, negative sti?ness on an electrical joint manipulator the change on active RoM and controllability of the ankle joint by di?erent levels of stiffness compensation is assessed. Ten healthy and two UMND patients participated in this study. Results: Active dorsi?exion RoM increased with 27.81% with the largest negative stiffness (50%) compensation (p=0.001) compared to the RoM in normal (0%) compensation. Muscle activation did not differ between the conditions. Jerk of the ankle was 59.51% (p