In this investigation we put forth a simple model to quantify the capacity of series elasticity to increase peak power output from an actuator. Using a linear bandwidth limited force source, we show how series spring stiffness and source stroke length effect power output to an inertial load. We show that an appropriate spring constant increases the peak power delivered to the inertial load over a limited stroke. The series elasticity changes the actuator operating point along its force-velocity curve and therefore effects the actuator work output over a fixed stroke length. For single shot motions, the peak power can increase by a factor of radic2 for appropriate series spring stiffness. We also present an example of how this work relates to human ankle function and it implies for the design of robotic or prosthetic ankles