Degeneration or inflammation of the plantar fascia, a web-like ligament that links the heel to the toes. Symptoms: Pain under the heel or towards the back of the foot�s arch, especially on your first steps of the day. Common causes: Stiff, immobile feet and calves, weak foot muscles, poor running technique and inppropriate footwear are frequent contributing factors. Plantar fasciitis is really nasty as the onset can be quite slow then its so difficult to get rid of. You need to stop running and get specialist treatment as soon as possible . Swimming and cycling are good alternatives to keep fit. It is essential to get treatment as the injury can be still there after rest. The problem often stems from tight calfs so you should see a sports massage therapist or a physiotherapist. They need to apply deep masssage to all areas of your calf and you need to have this done frequently at first then fairly regularly to keep your calfs supple. They need to apply the massage both whilst your leg is straight and then whilst bent to 90 degrees to reach deeper muscles. You can also get a "night splint" or "night sock" online which can help. You will almost certainly find it painful when you take your first steps on a morning. What happens is the because the fascia is tight it pulls on the calcanious bone in your heel. Your brain sends a message that makes you scrunch your feet up whereas what is really needed is it to be stretched so that your foot goes upwards towards your leg. The scrunch movement makes it worse. The night splint keeps the foot streched in the right way and the foot becomes less painfull when you first walk . You are supposed to wear them at night, but they are uncomfortable so its better to just wake 15 mins early and put it on for that time. You can also massage the fascia itself to loosen it. Rolling it over a squash ball is effective for this.