Improper positioning can also hamper blood flow to any body part. Prolonged sitting on an unpadded surface can obstruct the large blood vessels behind the knees, as well as damage the nerves, causing loss of sensation. Impaired blood flow can also lead to blood clot formation. Lack of fluid intake may increase the risk of clotting of the blood. Although serious, this complication is usually preventable.
Inactivity can also cause fluid retention and swelling of extremities.
Urinary tract Urinary tract infections are another risk for people who may spend long periods of time on their back. This can promote urinary stasis or stagnation in the flow or urine from the kidneys to the bladder, and thus, lead to infection. Prolonged immobility also causes an increase of minerals and salts to circulate in the blood that can promote the formation of kidney stones. Constipation is a common problem that may result from decreased physical activity. Other factors may aggravate bowel evacuation.