I have very tender achilles heal after sitting for a while. what is it from?

Symptoms are of Archilles tendonitis:

Achilles tendonitis is a condition of irritation and inflammation of the large tendon in the back of the ankle. Achilles tendonitis is a common overuse injury that tends to occur in middle-age recreational athletes. The overuse causes inflammation that can lead to pain and swelling. Furthermore, Achilles tendonitis can lead to small tears within the tendon, and make it susceptible to rupture.

What causes Achilles tendonitis?
The two most common causes of Achilles tendonitis are:

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  • Lack of flexibility

     

  • Overpronation