You see a skeleton in a lab, and they need wires to hold the spine in place. Well, in your body the wires are muscles. When there is a loosening on one side, your pelvis tilts. A spasm occurs when this tilt results in one side of the body supporting more weight than the other. Look at a telephone pole. If the supporting wire on one side is slack and loose, then the wire on the other side becomes tense and tight. In the case of the body, this is the muscle. And it will give you pain. If a man weighs 180 pounds and one side of him supports 90 and the other side 90, he is able to function. If one side supports 110 and the other supports only 70, a problem arises. For one thing, your leg on one side is shorter than the leg on the other.