Exemplary embodiments herein relate to a unique 4-bar linkage transmission provided between two adjacent links of a powered augmentation device that provides a varying mechanical advantage. Due to the kinematics of the linkage, the mechanical advantage between the actuator and the augmented joint varies with the position of the linkage. Thus, a high mechanical advantage can be provided in positions at which relatively high joint torque is required, and low mechanical advantage in positions at which relatively high joint speed is required. Consequently, the speed-torque (or velocity-force) operating area of the actuator can be consolidated by mapping the widespread output regions onto a smaller input region. This allows the actuator to be optimized for a narrower range of usage.