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.[2][relevant?]
[citation needed] During the stance phase, or when standing on one leg, the weakened abductor muscles (gluteus medius and minimus) on the side of the supporting leg allow the opposite hip to droop.
To compensate, the trunk lurches to the weakened side to maintain the center of gravity over the supporting leg.
If, when standing on the right leg, the left hip drops, it is a positive right Trendelenburg sign (the opposite side drops because the hip abductors on the right side do not stabilize the pelvis to prevent the droop).
[3] The patient exhibits an excessive lean in which the upper body is thrust to the right to keep the center of gravity over the stance leg.