A heel spur occurs when calcium deposits build up on the underside of the heel bone, a process that usually occurs over a period of many months. Heel spurs are often caused by strains on foot muscles and ligaments, stretching of the plantar fascia, and repeated tearing of the membrane that covers the heel bone. Heel spurs are especially common among athletes whose activities include large amounts of running and jumping. Heel spurs often cause no symptoms but can be associated with intermittent pain, especially while walking, jogging, or running. Sharp pain in the heel can also be experienced when standing after sitting for a long period of time. Heel spurs can be a result of plantar fasciitis.