The force generated by a polypyrrole (PPy) actuator operating under isometric conditions has been shown to decrease as the preload force applied to the actuator increases. The origin of the decrease in the force generated was found to be the change in modulus that occurs upon electrochemical stimulation of the polypyrrole. A simple analytical model is introduced to describe these effects. The relationship between the force generated and the actuator strain is explained using this model for both isometric and isotonic modes of operation. In addition, different means for bundling PPy fibres were investigated to optimize both the isotonic strain and the isometric force generated.