Sartorius

legsMusculus sartorius

The sartorius is the longest muscle in the human body — a thin strap running diagonally from the front of your hip across the thigh to the inside of your knee. It is the muscle that crosses your legs.

The sartorius runs from the bony point at the front of your hip, diagonally down and across the front of the thigh, to the inside of the knee. It is the longest muscle in the body, and it is easy to see on a lean leg as a thin ridge running across the thigh at an angle when the hip is flexed and turned out.

Because it crosses the thigh diagonally, its actions are an unusual combination: it flexes the hip, turns the thigh outward, pulls it out to the side, and bends the knee, all at once. Put those together and you get the movement of crossing one leg over the other — which is where the name comes from, sartor being Latin for tailor, after the cross-legged position tailors once worked in.

It attaches below the knee as part of the pes anserinus, alongside gracilis and semitendinosus, so it also turns the lower leg inward when the knee is bent.

It is a landmark as much as a muscle. Its inner edge forms the outer boundary of the femoral triangle at the top of the thigh, and it divides the front of the thigh into compartments that anatomical descriptions are organised around.

It is thin and produces little force. No exercise database names it, because no exercise targets it — its page here is an anatomy page rather than a training page.

Training notes

There is no sartorius exercise and there does not need to be one. It assists during any movement combining hip flexion with turning the thigh out, and during knee flexion, and that assistance is all it contributes.

It works during lunges, step-ups and any single-leg movement where the thigh has to be controlled in more than one plane at once, and during the swing phase of running.

Its visible contribution is the thin diagonal line across the front of the thigh on a lean leg — a shape feature rather than a mass one, and one that shows up when body fat is low rather than when the muscle is trained.

Anatomy

Origin
  • Anterior superior iliac spine and the upper half of the notch below it
Insertion
  • Upper part of the medial surface of the tibia, anterior to gracilis and semitendinosus in the pes anserinus
Actions
  • Flexes, abducts and laterally rotates the thigh at the hip
  • Flexes the leg at the knee
  • Medially rotates the leg when the knee is flexed
Innervation
Femoral nerve (L2–L3)

Sartorius is a narrow ribbon-like muscle arising from the anterior superior iliac spine and passing inferomedially across the anterior thigh to insert on the upper medial surface of the tibia. It is the most anterior of the three tendons forming the pes anserinus, lying in front of gracilis and semitendinosus.

Its oblique course means it crosses both the hip and the knee and acts in several planes at once: at the hip it flexes, abducts and laterally rotates; at the knee it flexes and, with the knee flexed, medially rotates the leg. The combined movement approximates the cross-legged sitting position from which its name derives.

It is a principal landmark of the anterior thigh. Its medial border forms the lateral boundary of the femoral triangle, and further distally it roofs the adductor canal, through which the femoral vessels and the saphenous nerve pass.

It is thin and its physiological cross-sectional area is small relative to its length, so its force contribution to any of its actions is minor compared with the prime movers it accompanies.

Under load

It is recruited as an accessory to hip flexion, hip abduction and knee flexion, and is not the prime mover in any of them.

No exercise in the imported database names it, and none targets it. Its involvement is incidental to lunging, stepping and single-leg loading in general.

Its surface visibility on a lean thigh is a matter of its superficial position rather than of hypertrophy.

Exercises

No exercise in the library names Sartorius yet. Nothing has been invented to fill the gap — a false reference costs more than an absent one.

Antagonists

Synergists