Tight and inflexible hamstrings receive a lot of attention as a cause of lower back pain, but weak hamstrings can also be the source. The hamstring is actually a set of three muscles that run from the pelvis to the knee at the back of the thigh. These muscles are used to facilitate bending the knee behind the midline of the body while the hip is extended, such as when running or walking. The group also helps keep the knee aligned.
Tense quadriceps and weak hamstrings are a common muscle imbalance. We tend to use our quadriceps more in everyday life, and many popular gym workouts emphasize isolated quadriceps development. There are two main ways that weak hamstrings can cause back pain.
The hamstrings work with the quadriceps to stabilize the movement of the knee and pelvis. This requires the muscles to be equal in strength, length and flexibility. If the hamstrings are weaker than the quadriceps, the pulley system formed by the muscles is impaired. The shorter, tighter quadriceps will pull down into the pelvis in front and up into the knee, as the hamstrings are too weak to exert a counterweight pull.
When the pelvis is pulled down in front, the lower back arches inward. This is called hyperextension of the lumbar spine. Tight hip flexors and erector spinal muscles in the lower back often accompany weak hamstrings because of this postural change. As vertebral angles change in the spine, there is increased pressure placed on the back of the vertebral discs, which can lead to premature disc wear, bulging, or herniation. These disk changes can cause sciatica.
Weak hamstrings can quickly turn into tight tendons. Weak muscles tire quickly due to lack of strength, and tired muscles contract to protect themselves from further use. This forced tensioning of the muscle creates a situation conducive to tension; the quadriceps kick into action before the hamstring recovers and stretches. A hamstring strain, strain, or tear may occur.
When the hamstring is injured, the body naturally compensates for it by employing other nearby muscles to do the work the hamstrings normally do. The muscles in the lower back can be activated when the leg is moved, although this action is beyond their natural duties. The muscles in the back and hips that compensate for the hamstrings can become sore and tense.
Signs of Hamstring Weakness
There are some symptoms that point to the hamstrings as the cause of back pain. If your hamstrings are weaker than your quadriceps, you may notice that your buttocks bulge and that you have an exaggerated lumbar arch.
If you have localized pain in the hamstrings and lower back, then a tension in the hamstrings is indicated.
Another sign of quadriceps/hamstring imbalance is the click or snap of the knee when the knee is bent or straightened.
Prevention and Treatment
Hamstring weakness and injury can be avoided with an exercise regimen that includes strengthening and stretching the muscle group, balanced with strengthening and stretching the quadriceps. See http://www.youtube.com/watch?v=QGTcgPVexrI for a series of exercises for the hamstrings. See 4 Hamstingstretch Stretches at http://physicaltherapy.about.com/od/flexibilityexercises/a/hamstingstretch.htm.
The treatment of well-established muscle imbalances requires a combination of myofascial release and targeted exercise. If the quadriceps have been chronically tense, they will need to be forced to relax and stretch again. Foaming at home or myofascial release performed by a physician can do this. Once the quadriceps have regained elasticity, the hamstrings can be developed.
Thigh tendon strain can usually resolve with a brief period of rest and ice. The above steps will need to be taken in addition to rest and ice to avoid further injury if a muscle imbalance is responsible for the tension.
It is important to understand that weak hamstrings can be the cause of back pain and hamstring strain. Keeping your body in balance will help resolve the pain in your lower back.