Tight, inflexible hamstrings get a lot of attention as a cause of lower back pain, but weak hamstrings may also be the source. The hamstring is actually a set of three muscles that run from the pelvis to the knee in the back of the thigh. These muscles are used to facilitate the bending of the knee behind the midline of the body while the hip is extended, such as when running or walking. The group also helps to keep the knee aligned.

Tight quadriceps and weak hamstrings are a common muscle imbalance. We tend to use our quads more in everyday life, and many popular exercises at the gym emphasize the isolated development of quads. There are two main ways in which weak hamstrings can cause back pain.

1. Biomechanical

Hamstrings work with the quadriceps to stabilize movements of the knee and pelvis. This requires that the muscles are equal in strength, length and flexibility. If the hamstrings are weaker than the quadriceps, then the pulley system formed by the muscles is disrupted. The tighter, shorter quadriceps will pull downward on the pelvis in front and upward on the knee, since the hamstrings are too weak to exert a counterbalancing pull.

When the pelvis is pulled down in front, the lower back arches inward. This is called hyper-extension of the lumbar spine. Tight hip flexors and erector spinae muscles in the lower back often accompany weak hamstrings because of this postural change. As vertebral angles change in the spine, there is an increase of pressure placed on the back side of spinal discs, which can lead to premature disc wear, bulging or herniation. These disc changes can cause sciatica.

2. Fatigue

Weak hamstrings can quickly turn into tight hamstrings. Weak muscles tire quickly due to their lack of strength, and tired muscles go into contraction to protect themselves from further use. This forcible tightening of the muscle sets up a ripe situation for strain; the quadriceps fire into action before the hamstring has recovered and lengthened. A pulled, strained or torn hamstring can result.

When the hamstring is injured, the body will naturally compensate for it by employing other nearby muscles to do the work the hamstrings normally do. Lower back muscles may be called into action when the leg is moved, though this action is beyond its scope of natural duties. The muscles in the back and hips that compensate for hamstrings can become sore and strained.

Signs Of Hamstring Weakness

There are a few symptoms that point to hamstrings as the cause of back pain. If your hamstrings are weaker than your quadriceps, you may notice that your bottom sticks out and that you have an exaggerated lumbar arch.

If you have localized pain in the hamstring and pain in the lower back, then a strained hamstring is indicated.

Another sign of a quadricep/hamstring imbalance is clicking or cracking of the knee when it is bent or straightened.

Prevention and Treatment

Hamstring weakness and injury can be prevented by pursuing an exercise regimen that includes both strengthening and stretching of the muscle group, balanced with strengthening and stretching of the quadriceps. See http://www.youtube.com/watch?v=QGTcgPVexrI for a number of hamstring exercises. See 4 hamstring stretches at http://physicaltherapy.about.com/od/flexibilityexercises/a/hamstingstretch.htm.

Treating a well-established muscle imbalances requires a combination of myofascial release and targeted exercise. If your quads have been chronically tight, they will need to be forced to relax and re-lengthen. Foam rolling at home or myofascial release performed by a practitioner can accomplish this. Once the quadriceps have regained elasticity, the hamstrings can be developed.

A pulled hamstring can usually be resolved with a brief period of rest and ice. The above steps will need to be taken in addition to rest and ice to prevent re-injury if a muscle imbalance is responsible for the strain.

It is important to understand that weak hamstrings may be at the source of back pain and hamstring strain. Keeping your body in balance will help to resolve lower back pain.