During the motion of walking, an upward movement of the pelvis, one side then the other, is required to let the leg follow through. The faster or longer each step the pelvis adjusts accordingly. The flexibility within the knees, ankles and hips are stabilized by the pelvis. Normal gait tends to minimize displacement of centre of gravity whereas abnormal gait through pelvic instability tends to amplify displacement. During pregnancy there may be an increased demand placed on hip abductor, hip extensor, and ankle plantar flexor muscles during walking. To avoid pain on weight bearing structures a very short stance phase and limp occurs on the injured side(s), this is called Antalgic Gait .