The plantar fascia is the thick tissue that runs from the front of your heel, over the arch of your foot, to the back of the ball of the feet. It is tough tendinous tissue that is designed to absorb shock as you transfer your weight from heel to toe. Its strength is maximal along its length and for most of us it can bear three times our body weight along its longitudinal axis. It is not as strong when twisted though.
Misuse, whether that be overstretch or twist will result in fibres exceeding their breaking strain and letting go. As this is tendinous tissue it does not have a ready blood supply so healing can be slow.
We can misuse the plantar fascia not only when running but also when walking, and like so many running injuries, healing can be delayed by the repeated re-injuring of a healing tendon when walking.
Symptoms include - Pain in front of the heel , through the arch and rarely along the back of the balls of the feet. Morning stiffness is characteristic and the pain can come on a few hours after the injury.
The plantar fascia is a very strong piece of tissue so it does not rupture and this is one of many injuries that you can continue to run on (although it will be uncomfortable)
If you find that symptoms get worse a couple of hours after wearing a pair of shoes even when walking , this means your interaction with gravity through those shoes lead to a misuse of the plantar fascia - Those shoes may have - too high an arch (this provides a pivot point for twisting), have too high a heel -allowing for leverage to increase twisting moment, they may have too little rigidity as you walk allowing twist. The upshot of all this is - throw those shoes away as wearing them will delay healing dramatically.
The errors most common in developing PF is to be taking your weight on the Ball of the foot whilst landing ahead of your centre of mass. Yes, enthusiastic toe running. Supination (rolling through on the outside of the foot before transferring to the ball of the foot for "toe-off" and pushing the ball of the foot into the ground at toe off. As you can see these are all errors of technique. Multiply the loads those errors produce by running too far too soon and when carrying too much weight and the pain will soon let you know your mistakes.
Another common cause is gripping of the toes as you run - this is more common in winter and when it is wet or frosty.
To cure(control) PF take these easy steps.
Walk lightly - imagine you are being pulled up and forward by someone lifting the armspits up and lengthening the back of your neck.
Walk with relaxed feet and let them go floppy as they pass by your supporting ankle
Shorten your stride, land with a bent knee and let the heels touch (you may even need to pull the toes up on landing to achieve this. This applies when walking and running
Do not push off - pull the ankle up under you instead.
Unweight the shoulder with each step - you can help this by swinging the upper torso over the new support foot with each step.
Avoid orthotics or arch supports as they can provide a pivot for the foot to promote twist.
The normal origin of the PF is the front of the heel and the insertion is the back of the Balls of the feet.
When exercising this you can promote healing by loading the toes and moving the heel around - Take you weight on the ball of the foot and movie the ankle around and around first one way then the other.
Place your hand over the toes so you hold the ball of the foot and resisting point the toes down letting your ankle rise rather than your toe descend (also using a stretchy cord to do this helps)
Repeat this exercise whilst pushing a finger into the Quaratus muscle (belluy of which can be found at the front of the heel on the inside of the foot at the back end of the arch. Massage this area afterward.
Jump up and down on the balls of the feet keeping the ankle locked at 90* degree angle at a cadence of 180-200x a minute.
Stretch and massage after any period of rest especially before weight bearing in the mornings.
Reduce your mileage and speed dramatically till healed
Useful other agents
Arnica at the initial stages
Cider vinegar and hot water soaks
golf ball to get into the quadratus muscle