Plantar fascia is the region of very thick connective tissue that lends support to the arch of the foot.  It extends from the calcaneus, or heel bone, to the metatarsal bones, or the toes.  When strained, due to either weight bearing problems or exercise degeneration, it leads to a very common condition and irritating condition known as plantar fasciitis.

There is still some debate in the medical community about how deep the plantar fascia should be considered to be.  Many separate the planta fascia from the deeper white connective tissue called the plantar aponeurosis; many medical dictionaries, however, hold that the plantar aponeuroisis is part of the plantar fascia.  The aponeorosis generally connects the outer muscles that form the plantar fascia, which are generally composed on long collage fibers that extend the length of the foot. 

The plantar fascia supports the foot by acting as something of pressure base.  The muscle area supports about 15% of the foot's entire weight, which is a considerable amount.  When too much is pressure is applied to the plantar fascia, then the muscles become overburden and strained, pulled taut between the heel bone and the bones of the toes.  This severe heel pain is what is commonly known as plantar fasciitis. 

The health of the plantar fascia is crucial to the maintenance of a healthy gait, which optimizes limb movement during exercise.  If the plantar fascia cannot handle the weight distribution of a normal gait, then it can limit the potential for exercise and physical labor, and cause pain in other parts of the body used to enable movement.