The paper presents a simultaneous force and length variation mode in shape memory alloy (SMA) robotic application. The robotic ankle contains four SMA actuators and a spherical articulation. In order to assure a high efficient robotic architecture, the mechanical and the control structure have to assure a real-time response to the work environment changes. The load variations or the difference between the moment of full contact step and the non contact moment for a waking robot are the standard situations for a SMA robotic ankle. The paper is divided in five sections. First section makes a short introduction in the physical description and conventional applications of shape memory alloy materials. Then, are presented the mathematical model for robotic ankle, the walking robot geometrical structure and the causality ordering of the active pair of legs, in this case with one free joint. In the last section some experimental results are presented. These results were obtained by using MATLAB programs, conceived by authors, for design and simulation of walking robots control algorithms.