The purpose of this study was to examine stiffness and modulus of elasticity of m. vastus lateralis. Thirty men and 27 women the members of Russian speed skating team participate in the experiment. Length, angle of fiber pennation, cross section areas, elongation of apponeurosis m. vastus lateralis, slack fiber length were determined by ultrasonography. Maximum isometric knee extension moment was determined by Biodex. Slack length of m. vastus lateralis fibers is in the range 0.25 - 0.35 cm and no significant differences between man and women. Rotation of fibers between rest length and maximum voluntary contraction about 6° from 12° to 18°. No significant differences between man and women tendon elongation (3 - 5 cm) and athlete qualification during maximum isometric knee extension. Elasticity modulus depends on sex and quality of athletes. The men speed skaters have maximum stiffness of tendo quadricipitis 5.5x10000 N/m. The lowest stiffness performed juniors women speed skaters - 3.5x10000 N/m.