Spring-mass models have been very successful in both describing and generating running behaviors. In this regard, the Spring-Loaded Inverted Pendulum (SLIP) is a useful model to represent hybrid dynamics of both natural and robotic runners. Existing research on dynamically capable legged robots, particularly those based on this model, generally considers improving in isolation the stability and control accuracy on the rough terrain or the energetic efficiency in steady state. On the other hand, the pure SLIP model is energetically conservative, hence being unable to define a way for modulation of running energy in legged robots. In this thesis, we propose a new method based on incorporating a virtually tunable leg damping onto the SLIP template model in order to control running energy while addressing both accuracy and efficiency. In the first part of this thesis, we present our theoretical approach and contributions showing that efficient and accurate control of running can be achieved by incorporating a tunable damping into the SLIP model. In the second part, our efforts towards experimental verification of these theoretical claims are presented.