Work-per-cycle calculations have been demonstrated for two modes of actuation behaviour: (1) working against a dead weight (isotonic actuation) and (2) working against a restoring spring. Importantly, the influence of the electrical stimulus on the elastic modulus of the actuator material has been included in the analysis. The change in elastic modulus is shown to significantly influence the actuator strain and work-per-cycle. The maximum work-per-cycle for each case has been calculated. Comparison of different materials has been made on the basis of our theoretical prediction and other published models. Work-per-cycle is shown to be significantly affected by the mode of loading.