Trendelenburg gait, named after Friedrich Trendelenburg, is an abnormal gait. It is caused by weakness or ineffective action of the gluteus medius muscle and the gluteus minimus muscle. Gandbhir and Rayi point out that the biomechanical action involved comprises a Class 3 lever, where the lower limb's weight is the load, the hip joint is the fulcrum, and the lateral glutei, which attach to the antero-lateral surface of the greater trochanter of the femur, provide the effort. The causes can thus be categorized systematically as failures of this lever system at various points.