A quadriceps control device comprises an elongated, elastic member having a first end affixed at an anterior position above the knee and a second end affixed at an anterior position below the knee of the user. The quadriceps control device may be utilized with a prosthetic or orthotic leg assembly. The quadriceps control device mimics to some degree the quadriceps muscle group in human anatomy, to thereby enhance the ability of a user of a prosthetic or orthotic leg assembly to control knee extension and flexion.