Lower back pain with irritation of the L3, L4 nerve roots can cause pain and spasm in the rectus femoris and pain and spasm in this muscle will aggravate lower back pain.

This muscle is one of the four muscles termed the quadriceps muscles. The quadriceps are the muscles in the front of the thigh and are responsible for straightening the knee.

The rectus femoris arises from an area on the pelvic bone known as anterior superior iliac spine and the part of the bone just above the hip joint. It inserts at the upper border of the kneecap (patella) and also to the tubercle on the front of the shin bone (tibia). Its action is to bend the thigh upwards (hip flexion) and to straighten the knee (knee extension). It receives the L2-L4 nerve root supply through the femoral nerve.

Since rectus femoris is the only muscle of the quadriceps that crosses over the hip joint as well as the knee joint, this muscle is more vulnerable to trauma than the other three quadriceps muscles (vastus lateralis, vastus medialis and vastus intermedius).

When the hip and knees are bent as in sitting, crouching or squatting, rectus femoris and tensor fascia lata muscles are very tight at the hip and excessively stretched at the knee. This predisposes the muscles to get easily traumatized. Additionally, aging of the L3, L4 nerve root, injury, or irritation from presence of degenerative arthritis of the spine, slipped disc, bulging disc are also responsible for underlying neurogenic weakness in this muscle.

Since the quadriceps is essential for keeping the knee steady when going down steps, inclines and in the walking phase after the heel strikes the ground, weakness of the rectus femoris and the tensor fascia lata (which also has L4 nerve root fibers) can predispose the person to falls.

To strengthen the rectus femoris and tensor fascia lata muscles, the principle involves education starting first with shortening contractions of the spinal extensors from the neck to the lower back and the hip extensor muscles. The hip flexor tightness is secondary to imbalanced contraction of the hip flexor muscles such as rectus femoris, tensor fascia lata, adductor muscles and the iliopsoas muscles in the presence of weak back and hip extensors such as the gluteus maximus, lower part of the adductor magnus muscle and the hamstring muscles. When the knee is flexed, the hamstring muscles do not participate in straightening the hip (extension). Therefore most of the strength of the hamstrings is directed to bending the knee (flexion).

The health education for shortening contractions of the spinal extensors and hip extensor muscles such as gluteus maximus and adductor magnus must be performed first to return strength to these muscles. These extensor muscles are the main muscles constantly exposed to lengthening contractions at the hip making them weak.

At the knee, the weakness in the extension force results in unopposed pull of the knee flexor muscles. The shortening and spasm in the knee flexor muscles such as the hamstrings and the gastrocnemius muscles are difficult to release primarily. Therefore shortening contractions of the knee extensor muscles such as the rectus femoris, tensor fascia lata and the other three quadriceps muscles need to be performed first.

It is difficult to isolate these muscles to be individually trained for shortening contractions. Selective activation of these muscles is best performed with motor point stimulation using the eToims Twitch Relief Method.

Thus in the treatment of lower back pain and discomfort, rectus femoris has to be treated together with all the other large and powerful muscles that cross multiple joints and are exposed to lengthening contractions.