The plantar fascia is a band of strong tissue that in essence supports all of your body weight. It runs along the sole of the foot from the heel to the midfoot region.
As well as supporting your body weight it also acts as a shock absorber. Repeated burden from the above 2 functions can cause small tears and injuries to the fascia, particularly at its insertion point on the heel. The main causes are:
Pain under your heel and midfoot is the most common presentation which is usually worse in the morning and following activity.