Inverse dynamics model. An inverse dynamics model developed by DeVita and Hortobagyi was modified from a 2-D sagittal plane model (23) to a 3-D model that incorporates frontal plane knee forces and torques (24). This model was used to calculate compressive, anteroposterior shear, and resultant joint forces within the tibiofemoral compartment of the knee joint. A 3-D inverse dynamics analysis of the lower extremity was used to obtain the joint torques and reaction forces at the hip, knee, and ankle. These results, along with the kinematic description of the participants’ lower extremity and related anatomic and physiologic characteristics, were used to