The muscles and joints of the legs provide strength and stability for the body. These muscles serve to transmit the weight of the body and provide power for such common activities as walking, running, and jumping. They also absorb the cumulative impact of those activities. The leg bones are girded on all sides by sets of powerful muscles that allow the legs to bend (flexion) and straighten (extension) as well as move outward from the body (abduction) and inward (adduction). Some of these muscles are relatively long and participate in more than one type of movement.
Flexors (anterior):
The rectus femoris is one of the four bellies of the quadriceps muscle
group. The quadriceps muscle group consists of four muscles: the
rectus femoris, the vastus lateralis, the vastus intermedius, and the vastus
medialis. It is a large fleshy mass that covers the front and sides
of the femur bone (upper leg bone). The muscles work together as
the primary extensor of the knee. The rectus femoris is the only
two-joint muscle in the group, crossing both the knee and the hip joint.
It originates at the back of the inferior iliac spine and inserts in the
top of the patella (knee cap). This long, flat muscle extends the
leg at the knee joint and flexes the thigh at the hip joint. When
the rectus femoris is contracted, the knee joint is straightened and the
lower leg is extended. When it is relaxed, the lower leg is flexed
(bent at the knee).
The vastus lateralis is the largest of the quadriceps muscles. The quadriceps muscle group consists of four muscles: the rectus femoris, the vastus lateralis, the vastus intermedius, and the vastus medialis. They form a large fleshy mass that covers the front and sides of the femur (upper leg bone) and work as the primary extensor of the knee. The vastus lateralis occupies the outside of the thigh and extends partially around to the front and back of the thigh. It extends the lower leg at the knee joint and is used when rising from a squatting position.
The vastus medialis is the lowest of the quadriceps muscles. The quadriceps muscle group consists of four muscles: the rectus femoris, the vastus lateralis, the vastus intermedius, and the vastus medialis. These muscles form a large, fleshy mass that covers the front and sides of the femur (upper leg bone). They are the primary extensor of the knee. The vastus medialis is a bulging teardrop form located on the inner front corner of the lower thigh. It can be divided into two portions, the vastus medialis longus, which extends the knee, and the vastus medialis oblique.
The vastus intermedius is and extensive muscle that lies deep to all the other quadriceps bellies, adding muscular fullness under them. The quadriceps muscles consist of: the rectus femoris, the vastus lateralis, the vastus intermedius, and the vastus medialis. These muscles form a large fleshy mass that covers the front and sides of the femur (upper leg bone). They work together as the primary extensor of the knee.
The sartorius is the body's longest muscle. It is a long, narrow, ribbon-like muscle that spirals down the thigh. It begins on the front of the hip, where it originates at the front point of the pelvis (the tip of the anterior superior iliac spine), runs down and across the front of the thigh, and along the inner side of the knee where it is anchored on the upper end of the tibia. This muscle is a powerful flexor of the thigh. It helps bend both hip and knee and twist the leg allowing you to sit cross-legged.
The iliopsoas is actually the blending of two muscles, the large, flat triangular iliacus and the fusiform psoas major. It is considered a single muscle group that begins deep in the back of the abdomen and converges towards its insertion on the back of the femur (upper leg bone). It is a powerful flexor of the hip joint. It flexes the thigh when kicking, or the pelvis and trunk when doing sit-ups.
The psoas minor is a long, slender, weak muscle that assists in flexing the trunk and the lumbar spinal column. It lies just in front of the psoas major muscle.
The pectineus muscle lies on the front of the upper and middle part of thigh. It is a flat, quadrangular muscle that arises from the pectin pubis (pectineal line) and, to some extent, from the surface of the bone just in front of it. The pectineus flexes and moves the thigh towards the body and rotates it toward the center.
Extensors (posterior);
The biceps femoris is included with the hamstring muscles. It
is a large muscle comprised of two heads (two points of attachment to the
bone), the long head and the short head. The two muscles converge
to a single tendon of insertion. This common tendon is located on
the outer back corner of the knee and forms the outer hamstring.
Both heads of the muscle flex (bend) the lower leg at the knee joint and
rotate the tibia outward. The long head also assists with the extension
and outward rotation of the thigh at the hip joint, making it a two-joint
muscle, while the short head is a single-joint muscle.
The semimembranosus muscle is one of the hamstring muscles. It flexes the lower leg at the knee joint and rotates it in. It consists of a fleshy muscle belly with a tendon at each end. The muscle fibers extend downward from the knee to the middle of the outer condyle of the femur (upper leg bone). The tendon of the semimembranosus muscle, along with the semitendinosus and gracilis, form the inner hamstring.
The semitendinosus originates from the ischium (hip). Its long, narrow, fleshy belly ends two-thirds of the way down the thigh at its tendon. It sits in the muscular groove formed in the semimembranosus muscle at the inner back of the thigh. This muscle flexes the lower leg and extends the thigh at the hip joint. It is considered one of the hamstring muscles. Its tendon, along with the tendons of the semimembranosus and the gracilis, form the inner hamstring.
We sit on the most powerful and largest muscle in our body, the gluteus maximus. It is a thick, fleshy, quadrilateral muscle that forms the major volume of the buttock. The muscle descends downward and outward from its origin and wraps around the outer back corner of the pelvis. It connects the ilium, sacrum, and coccyx to the femur by tissues of the thigh. The gluteus maximus consists of coarse muscle fibers that powerfully extend (straightens) the thigh at the hip joint and moves it away from the body, as when walking or running. It is also used to raise the body from a sitting position.
The gluteus medius is a wide, fan-shaped muscle that tapers into a strong flattened tendon at its insertion on the femur (upper leg bone). It runs from the outer portion of the ilium (pelvis), up to the crest of the ilium. The gluteus medius is partly covered by the gluteus maximus. You can feel the crest of the gluteus medius through the skin. It moves the thigh outward and rotates it, as when walking or running. It keeps the torso upright during walking when one foot is touching the ground and the other is not touching the ground. The gluteus minimus lies just beneath the gluteus medius and works with it.
Deep rotators (posterior):
The quadratus femoris, as its name implies, is quadrilateral in shape.
It is a short, flat muscle that runs horizontally from the upper lip of
the ischium (hip) to the upper part of the femur (thigh bone). This
muscle helps rotate the thigh.
The gemelli (gemellus superior and gemellus inferior) are two small muscles of the hip. The gemellus superior is the smallest of the two muscles. The muscles arise from the spine of the ischium and insert into the great trochanter of the femur (upper edge of the thigh bone). These muscles help rotate the thigh.
The obturatorius externus is a flat triangular muscle covering the wall of the pelvis. The muscle fibers converge into a tendon which runs across the back of the hip joint and inserts in the femur (thigh bone). This muscle rotates the femur outward.
The obturatorius internus lies partly within the cavity of the pelvis and partly at the back of the hip joint. The muscle narrows into a single, flattened tendon at its point of insertion in the great trochanter of the femur (upper edge of the thigh bone). It helps rotate the thigh and steady it when sitting up.
The piriformis is a flat, pyramid shaped muscle lying partly in the pelvis and partly at the back of the hip joint. The muscle arises from the sacrum, passes through the sacrosciate foramen, and inserts as a round tendon into the upper edge of the great trochanter of the femur (upper edge of the thigh bone). This muscle helps rotate the thigh.
Abductors (lateral):
The iliotibial tract, also called the iliotibial band, is a long, wide,
band of fascia that lies over the muscles on the outer surface of the thigh.
It begins superiorly at the level of the greater trochanter of the femur
(upper edge of the thigh bone) and ends inferiorly where it inserts in
the condyle of the tibia. This band is a thickening of the normal
fascia that surrounds the entire leg. It is thin medially (inner
thigh), but is thick laterally (outer thigh). It helps hold the muscle
in place and aids in stability of the knee.
The tensor fascia latae is a short, thick, teardrop-shaped muscle that is located on the outer front corner of the ilium (pelvis). It connects the ilium to the tissues of the thigh. The muscle's form begins at the front point of the hip and ends where the muscle attaches to the iliotibial band. In the standing position, the belly becomes stretched into an elongated oval shape, but as the thigh is flexed, it changes into its characteristic teardrop shape. This muscle flexes, abducts, and medially rotates the thigh.
Adductors (medial):
There are three adductor muscles in the legs, the adductor longus,
the adductor brevis, and the adductor magnus. The three adductors
work with the pectineus to move the thigh inward. They are powerful
muscles that rotate the thigh outward and bring it across the opposite
side, as when crossing your legs. The adductor longus is a long triangular
muscle, originating with both fleshy fibers and a strong tendon from a
small area on the front of the pubic bone of the pelvis and inserts in
the femur (upper leg bone). The adductor brevis lies just behind
the adductor longus. The adductor magnus is a large triangular muscle
that forms a dividing wall between the muscles of the inner thigh and those
on the back of the thigh. It is located on the inside of the thigh.
This long muscle arises from a narrow point on the pelvis bone, passes
between the masses of the hamstring and quadriceps groups and ends, at
its wide apex, on the back of the femur. It is a powerful muscle
that adducts the thigh. The small uppermost portion of the adductor
magnus is called the adductor minimus.
The gracilis is a thin, wide, band-like muscle that sits on the inside of the thigh. It is wider at its point of origin at the edge of the midsection of the pubic bone and tapers at its insertion in the inside surface of the shaft of the tibia. This muscle brings the knee up and pulls it across the front, toward the middle of the body. It also assists in rotation of the leg.
Anterior thigh
quadriceps
superficial
quadriceps
deep
sartorius,
tensor fascia latae
adductor
longus, adductor magnus
adductor
brevis, pectineus, gracilis
femoral
triangle
Posterior thigh
biceps
femoris
semimembranosus,
semitendinosus
popliteal
fossa
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