A predictive model that can be used to estimate the isometric force response of the locust hind leg extensor muscle is presented. The model consists of two first order coupled differential equations. The first of these equations is linear and relates an input pulse train to the calcium concentration in muscle filaments. The second is non-linear and relates the calcium concentration to muscle force. Experimental data was collected by stimulating the extensor muscle and measuring the force generated at the tibia. Model parameters were estimated by minimising the error between the modelled and actual force response in a set of training data. These parameters were then used to predict the isometric response when the neural activity recorded during a kick was used as an input to the model. The model was found to accurately predict the isometric force response of the locust hind leg extensor muscle.