In this paper, we extend our previous work (Proc. Computer Animation and Simulation, pp. 125-135, Aug. 2000) and propose a muscle model that is suitable for computer graphics based on physiological and anatomical considerations. Muscle motion and deformation is automatically derived from one or several action lines, each action line being deformed by a 1D mass-spring system. The resulting model is fast, can accommodate most superficial human muscles, and could easily be integrated into current modeling packages. Example animations can be found at