Exactly what causes plantar fasciitis is not well understood. But it probably develops as the result of repeated small tears in the plantar fascia. Normally when you walk, your plantar fascia stretches as your foot strikes the ground. If the plantar fascia is strained by the way you walk or by repeated stress, it can become weak, swollen, and irritated (inflamed), and it can hurt when you stand or walk.
Conditions or activities that may lead to plantar fasciitis include:
Things that affect how the feet work (biomechanical factors). These include abnormal inward twisting or rolling of the foot (pronation), high arches, flat feet, tight calf muscles, or tight tendons at the back of the heel (Achilles tendons).
Repetitive activities, such as jobs that require prolonged walking or standing on hard or irregular surfaces or sports such as running.
Things that put extra stress on the feet, such as being overweight or wearing shoes that are poorly cushioned, don't fit well, or are worn out.
The natural process of aging. Plantar fasciitis is most common in middle-aged adults.