The femur, also known as the thigh bone, is the biggest, strongest, and longest bone in the human body. It is also the only bone in the upper leg. Because of this, it attaches to a lot of different muscles in the upper leg. These muscles are attached to the femur in order to make movements possible in the hip and knee joints. In total, 23 different muscles are attached to the femur. Some muscles are large and strong, like the gastrocnemius muscle, whereas other muscles are smaller, such as the popliteus muscle. Whether they’re big or small, all the muscles that attach to the femur play a role in the movement of the hips, legs, and knees.