Open-loop control strategies for legged robot locomotion have been investigated by many researchers because of the advantages in terms of simplicity and robustness, although the influence of control inputs to locomotion performance is not fully clarified. This paper investigates two of the most basic forms of control input, sinusoidal and pulsed signals, to be used in a class of hopping robot based on parallel elastic actuation. Our results show that a pulsed torque outperforms its sinusoidal counterpart with a lower energy expenditure. Moreover, the pulsed driving torque is capable of keeping the same energy efficiency while changing the forward hopping velocity, which is not possible with the sinusoidal driving torque. Such findings will help shape the future of robotics by achieving higher energy efficiencies within legged robots, while maintaining behavioural diversity.