The largest muscle masses in the leg are present in the thigh and the calf. The muscles that make up the quadriceps are the strongest and leanest of all muscles in the body. These four muscles at the front of the thigh are the major extensors (help to extend the leg straight) of the knee. They are: Vastus lateralis: On the outside of the thigh, this is the largest of the quadriceps. It extends from the top of the femur to the kneecap, or patella.