The Achilles tendon is a tendon formed by the confluence of the two gastrocnemius muscles of the calf and the soleus muscle.  During intense exercise such as running and jumping, the Achilles tendons are repeatedly pulled.  Severe inflammatory reactions will occur if the load is too large, the exercise is done too fast, if the calf muscles have insufficient strength or poor elasticity, if the Achilles tendons are too short, as well as due to hard field conditions, shoes, and other factors.