Lower Back Pain - The Role Of Hamstrings Lower back pain is most commonly from spinal nerve root L5 irritation followed by the S1 nerve root. Both nerve roots are strongly represented in the buttock muscle (gluteus maximus: predominant S1) and the inner thigh muscle (adductor magnus: the lower part L5, S1), hamstring muscles (L5 and S1), gluteus medius (predominant L5) and tensor fascia lata (predominant L5). There are two parts tto the long hamstring muscles, the outer part (has one lateral muscle) and the inner part has (two medial) muscles. There is also another muscle known as the short hamstring muscle. The long hamstring muscles arise from the pelvic bone area known as the ischial tuberosity (this bone is under the buttock muscle and we place pressure on this bone when we sit). Thus the long hamstring muscles come from above the hip. They end (insert) on the leg bones. The short hamstring muscle arises from below the hip from the thigh bone. The long hamstring muscles receive their nerve supply through the sciatic nerve whereas the short hamstring muscle is supplied by the common peroneal nerve
Whenever a muscle is tight, you must always consider the balance in strength between the muscles on opposite sides of the joint. In the case with the hamstrings, they act from behind to straighten the hip joint (extend) and bend the knee joint (flex). So the strength of the muscles in the front of the hip that bend the hip and thigh up (flex) and the muscles in the front of the knee that will straighten the knee (extend) are important to balance the action of the hamstrings. Therefore, if the muscles that straighten the hip joint (extensors) are weak, the muscles that bend the hip and thigh upward (flexors) will be automatically stronger. This itself will make the hip extensors (gluteus maximus, adductor magnus) weaker since they will now be stretched beyond their optimal length
Hamstring muscles do have an effect on straightening the hip, provided the knee is straight. However, when we are sitting down, the hamstring muscles do not have much effect on straightening the hip (extension). The action of the hamstrings will therefore be most prominent for bending the knee. The sitting position with knees bent thus puts the hamstring muscles to become short and tight behind the knee.
The sitting position also puts the rectus femoris and tensor fascia lata muscle at the front of the knee to be stretched across the knee. Since these muscles straighten the knee, they will be stretched beyond optimal length when the knee is in a bent position such as in sitting. This stretch effect is made worse since both these muscles are already shortened when the person sits since these two muscles are responsible for bending the hip also.
The setting for the tightness of the hamstrings at the knee thus stems from weakness of the lower back muscles and the muscles that surround the hip from behind (gluteus maximus, adductor magnus) and from the outer aspect (gluteus medius and tensor fascia lata).
Therefore tightness of the hamstring muscles cannot be accomplished just by stretching the hamstring muscles. Shortening contractions have to be performed to muscles constantly exposed to lengthening contractions. These include perform shortening contractions to the spinal muscles from neck to the base of the spine. At the hip, shortening contractions have to be performed to the gluteus maximus and adductor magnus muscles which have nerve related muscle weakness in the presence of constant exposure to lengthening contractions