We investigate the problems of asymptotic stabilization and output regulation of a biomimetic actuation system which independently modulates position and net stiffness. We show how the passivity formalism and the technique of input saturation developed by Lin (1995 and 1996) can be used to asymptotically stabilize this mechanical system over its feasible domain via bounded feedback. Two output regulators, a linear PIE controller and a feedback linearizing controller, an developed. The performance of the proposed controllers is illustrated through numerical simulation.