Right before you stand on one leg, your abdominal muscles tighten. Then the deep muscles of the low back contract to stiffen and protect the spine. The muscles and ligaments work together in the low back and pelvic area to hold them steady. Your body weight can now shift over to the standing leg.
The central nervous system controls the timing and pattern of muscle contraction for movements of this kind. The muscles squeeze and hold the joints of the pelvis together. This allows the load of your weight to be shifted between the spine and the legs. Everything must work in a certain order to allow smooth movement.
But what if a person has sacroiliac (SI) joint pain? Do the muscles still contract in the same order to keep the pelvis stable? Researchers compared muscle patterns in 14 men with SI pain to 14 men with no SI pain. Muscle patterns of the standing leg were measured as each man picked one leg up to bend the hip 90 degrees.
Researchers found a delay in abdominal, low back, and hip muscle contraction in the men with SI pain. At the same time, part of the hamstring muscle behind the thigh contracted early compared to men with no SI pain. These changes occurred on both sides, not just the side of the painful SI joint.
It’s helpful to know that changes occur in how and when low back, hip, and abdominal muscles contract with SI joint pain. The authors of this study conclude that further research is needed to find out if exercise can restore normal muscle patterns as a treatment for SI joint pain.