Achilles TendonitisThis is another common injury that many runners suffer from
. The achilles tendon is located at the back of your lower leg. The tendon becomes stiff and sore around the area of the heel. Stiffness tends to increase due to lack of movement or the leg has been resting. For example, people with tendonitis feel more stiffness in the heel area after waking up from sleep in the morning time.