The proper Latin plural form of the adjective quadriceps would be quadricipites. In normal English usage, quadriceps is used in both singular and plural. The singular form quadricep, although incorrect, is frequently used.

It is subdivided into four separate portions or 'heads', which have received distinctive names:

All four parts of the quadriceps muscle attach to the patella (knee cap) via the quadriceps tendon.

All four quadriceps are powerful extensors of the knee joint. They are crucial in walking, running, jumping and squatting. Because rectus femoris attaches to the ilium, it is also a flexor of the hip. This action is also crucial to walking or running as it swings the leg forward into the ensuing step. The quadriceps, specifically the vastus medialis, plays the important role of stabilizing the patella and the knee joint during gait.

In strength training, the quadriceps is trained in isolation with the leg extension exercise, as well as a part of several other lower body exercises. In many sports, it is important to have strong quadriceps muscles; if not, they are commonly torn.

Knee diagram

Capsule of right knee-joint (distended). Lateral aspect.

Cross-section through the middle of the thigh.

Anterior aspect of right leg.

Front and medial aspect of right thigh.