Lower back pain caused by S1 nerve root irritation will affect the hip extensor muscles which S1 nerve root so richly supplies.
The hip extensor muscles are best tested by having the patient lie facedown. The patient bends the knee and lifts the knee off the surface of the bed. The examiner can test the strength of the gluteus maximus muscle by pushing down on the buttock and thigh toward the bed while the patient resists the hip from moving down.
If the patient lifts the hip and thigh off the surface of the bed with the knee straight, this movement is primarily performed by the hamstring muscles.
The muscles which perform hip extension are:
- gluteus maximus (inferior gluteal nerve carrying L5, S1 root fibers primarily S1)
- biceps femoris, long head (sciatic nerve carrying L5, S1 root fibers primarily S1)
- semitendinosus (sciatic nerve carrying L5, S1 root fibers primarily L5)
- semimembranosus (sciatic nerve carrying L5, S1 root fibers primarily L5)