The quadriceps femoris (Latin for “four-headed of the femur”), also called simply the quadriceps, quadriceps extensor, quads, is a large muscle group that 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 the strongest and leanest muscle in the human body.
The quadriceps is also involved in Lombard’s Paradox.
The proper plural form of the adjective quadriceps is quadricipes, a form not in general use; instead, quadriceps is used in both singular and plural (i.e., when referring to both legs). The form quadricep , though common even in professional contexts, is incorrect. The error may derive from a mistaken belief that quadriceps is a plural noun (rather than an adjective in the singular), since English typically forms its plurals with the addition of the letter s to the end of a word stem.
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.
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.
This article was originally based on an entry from a public domain edition of Gray’s Anatomy. As such, some of the information contained within it may be outdated.


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