art IV begins the study of the lower extremity. Chapters 11 through 13 examine the structures and functions of the leg joints. Chapter 14 explores concepts related to human locomotion and gait. In contrast to the upper extremity, which functions mainly in open chain mobility activities, the lower extremity functions mainly in closed chain activities. The muscles and joints of the lower extremities provide the power and strength to lift the body from a sitting to a standing position and to control the entire body weight in ascending or descending stairs. They also provide the muscle contractions needed to propel the body weight during walking short and long distances. Chapter 11 introduces the hip complex, which is formed by the pelvis and the femur. Chapter 12 looks at the structures related to the knee complex, made up of the tibiofemoral and patellofemoral joints. Chapter 13 examines the multiple joints of the ankle and foot and their interrelationships during various activities. Collectively, the information in Part IV summarizes how each joint in the lower extremity affects the alignment and function of the other joints.
Part IV concludes with the study of the components of human locomo- tion and the role each joint plays during walking. It is essential to under- stand that each of the joints in the lower extremity chain is interdependent on the other joints. Part IV lays the foundation for understanding how each component of the leg contributes to the total function of the extremity and the role the lower extremity plays in the function of the entire body. The chapters look at the function of the lower extremity during both closed and open chain work to move the body from one position to another and across level and unlevel surfaces when performing daily activities such as dressing and driving, work duties, and participating in sports and leisure pursuits.
