A muscle that can move its point of origin towards its point of insertion. Muscles usually move their insertion towards their origin. For example, the gluteus maximus works in the normal manner when it extends the hip joint: when the leg is pulled backwards, the insertion on the femur moves towards the origin on the pelvis, which remains stationary. However, it exhibits a reverse action when the trunk is bent forwards: the gluteus maximus pulls the trunk upright by moving its origin on the pelvis towards its insertion on the femur, which remains stationary.
Subjects: Sports and Exercise Medicine.