If the straight leg raise is done actively by the patient, it is a test of functional leg strength, particularly the rectus femoris element of the quadriceps (checking both hip flexion and knee extension strength simultaneously).

If carried out passively (also called Lasègue's sign, Lasègue test or Lazarević's sign), it is used to determine whether a patient with low back pain has an underlying nerve root sensitivity, often located at L5 (fifth lumbar spinal nerve).

[2] In order to make this test more specific, the ankle can be dorsiflexed and the cervical spine flexed.

A meta-analysis reported the straight-leg test as having:[5] If raising the opposite leg causes pain (cross or contralateral straight leg raising): Lasègue's sign was named after Charles Lasègue (1816–1883).

[6] In 1864 Lasègue's medical student J.J. Forst described the signs of developing low back pain while straightening the knee when the leg has already been lifted.