Plantar Fasciitis is caused by excessive stretching of the fibrous tissue that is present at the bottom of the foot.  This excessive stretching can lead to heel/arch pain, and heel spurs. Flat feet (over-pronation) are the leading cause of plantar faciitis. Plantar Fasciitis can be aggravated or caused by: an unusually high arch, sudden changes in physical activity, ill-fitted shoes, obesity and the weight gain associated with pregnancy.