Excessive pronation of the foot (over 5 degrees) in the subtalar joint is a type of mechanical mechanism that can lead to tendinitis.An overuse injury refers to repeated stress and strain, which is likely the case in endurance runners. Overuse can simply mean an increase in running, jumping or plyometric exercise intensity too soon. Another consideration would be the use of improper or worn-down footwear, which lack the necessary support to maintain the foot in the natural/normal pronation. Pathophysiology
The Achilles tendon is the extension of the calf muscle and attaches to the heel bone. It causes the foot to extend (plantar flexion) when those muscles contract.The Achilles tendon does not have good blood supply or cell activity, so this injury can be slow to heal. The tendon receives nutrients from the tendon sheath or paratendon. When an injury occurs to the tendon, cells from surrounding structures migrate into the tendon to assist in repair. Some of these cells come from blood vessels that enter the tendon to provide direct blood flow to increase healing. With the blood vessels come nerve fibers. Researchers including Alfredson and his team in Sweden  believe these nerve fibers to be the cause of the pain - they injected local anaesthetic around the vessels and this decreased significantly the pain from the Achilles tendon. Diagnosis
Achilles tendinitis is usually diagnosed from a medical history, and  physical examination of the tendon. Projectional radiography shows calcification deposits within the tendon at its calcaneal insertion in approximately 60 percent of cases.
Another risk factor is any congenital condition in which an individuals legs rotate abnormally, which in turn causes the lower extremities to overstretch and contract; this puts stress on the Achilles tendon and will eventually cause Achilles tendinitis. References


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