Sartorius

Pronunciation: sar-TOR-ee-us

Structure & function

Location

The longest muscle in the body, a thin strap running diagonally across the front of the thigh from the outer hip to the inner knee.

Origin

Anterior superior iliac spine (ASIS) of the hip bone.

Insertion

Upper medial surface of the tibia.

Main action(s)

Flexes, abducts, and externally rotates the thigh at the hip, and flexes the knee — the combination of actions used to sit cross-legged (historically the position of a tailor at work, giving the muscle its name).

Joint(s) crossed

Hip joint and knee joint

Movement plane

multiple

Innervation

Femoral nerve (L2–L3)

In daily movement

Crossing one leg over the other while seated, or the outward-turning, knee-lifting motion of stepping over an obstacle.

In exercise

A synergist rather than a prime mover in most lower-body exercises; assists hip flexion/external rotation movements.

Commonly confused with

Its diagonal path is often confused with the tensor fasciae latae's, but the sartorius runs to the INSIDE of the knee while the TFL/IT band runs to the OUTSIDE.

Common misconceptions

There is no dedicated 'sartorius exercise' in typical training — it is trained incidentally through hip-flexion and rotation movements.