This letter presents derivation and experimental evaluation of extended dynamical model of twisted string actuator (TSA). The proposed model supports more precise estimation of required motor torque for both low-speed and high-speed (up to 2 & x00A0;Hz) motion by considering effects of elastic deformation of strings and frictional forces. Analysis of the experimental data demonstrated that the relative error between theoretical and practical curves never exceeded 7 & x0025; for the whole range of tested motion frequencies, the accuracy that is impossible to achieve with state-of-art mathematical models. The proposed dynamical model can be used for accurate model-based control of the TSA-based systems and for efficient TSA motor selection.