Julie Corliss is the executive editor of the Harvard Heart Letter. Before working at Harvard, she was a medical writer and editor at HealthNews, a consumer newsletter affiliated with The New England Journal of Medicine. She … See Full Bio
Dr. Christopher P. Cannon is editor in chief of the Harvard Heart Letter. He is a professor of medicine at Harvard Medical School, and senior physician in the Preventive Cardiology section of the Cardiovascular Division at … See Full Bio
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The straight leg exercise is often used in Physical Therapy to help patients improve the strength of their lower extremities.
Over the past 34 years as a Physical Therapist (Physiotherapist), I have often prescribed the straight leg raise exercise to patients recovering from a variety of surgeries or traumas to their body. It is a popular exercise that can be done before you are able to place full weight on a joint or limb. The straight leg raise is a cornerstone exercise in rehabilitation for knee replacements or many surgeries involving the lower leg, foot and ankle.
As the name implies, the straight leg raise exercise does not require you to bend the knee joint. This is encouraged when an individual has advanced arthritis in their knee(s). The straight leg raise exercise strengthens the muscles of the upper thigh, the quadriceps, without placing any stress on the knee joint.
Although the straight leg raise exercise is kind to the knee, it can be hard on the low back. The reason back pain can occur is because the hip flexor muscles work along with the quadricep muscles to raise the leg up. Engaging the hip flexors without counteracting some of its effects can lead to back pain. Let me explain why this happens.
The quadricep muscles attach from the front of the pelvis and upper thigh to below the knee. This is illustrated in the image to the right.
If you only had to engage your quadricep muscles to raise your leg, you would not have to worry about compromising your low back.
However, the act of doing a straight leg raise exercise also involves a powerful hip flexor muscle, known as your iliopsoas.
The psoas part of the hip flexor muscle originates from the front of the spine, and it joins the iliacus before attaching onto the upper thigh. The psoas major and psoas minor as well as the iliacus muscles can be seen near the top of the image to the right.
The pull from psoas at it’s spinal attachment points (caused by raising the leg) can cause you to arch your lumbar spine area. This back arch, in turn, can lead to back pain. You must counter the back arch by engaging your deep abdominals. Activating your deep abdominal muscles will counter the strain on the lower (or lumbar) spine and reduce the chance of back pain.
[Image attribution. Henry Vandyke Carter [Public domain]]