Quads

For other uses see Quad
The quadriceps femoris (quadriceps, quadriceps extensor, guads or quads) includes the four prevailing muscles on the front of the thigh. It is the great extensor muscle of the knee, forming a large fleshy mass which covers the front and sides of the femur.
It is subdivided into separate portions, which have received distinctive names.
Rectus femoris occupies the middle of the thigh, covering most of the other three quadriceps muscles.It is named from its straight course.

The other three lie deep to rectus femoris and originate from the body of the femur, which they cover from the trochanters to the condyles:
Vastus lateralis is on the lateral side of the femur.
Vastus medialis is on the medial side of the femur.
Vastus intermedius lies between vastus lateralis and vastus medialis on the front of the femur.

All four parts of the quadriceps muscle attach to the patella via the quadriceps tendon.
The quadriceps is also involved in Lombard's Paradox.
Actions
All four quadriceps are powerful extensors of the knee joint. Because rectus femoris attaches to the ilium, it is also a flexor of the hip.