PIR results from a neurological feedback through the spinal cord to the muscle itself when an isometric contraction is sustained, causing a reduction in tone of the muscle which has been contracted. This reduction in tone lasts for approximately 20–25 seconds, during which time the tissues can be more easily moved to a new resting length.

The pubic symphysis is composed of strong ligaments which hold the pubic rami together but which soften during pregnancy due to hormones and which separate slightly to allow for the passage of the baby from the pelvis.

Because sitting alters the muscle lengths in the legs so greatly, the lower half of the body no longer gives muscular support to the cardiovascular system. The calves and hamstrings become so tight they cannot hold their share of blood, causing excess strain on the main arteries, increasing the risk for cardiovascular disease. The evil henchman Sit