When you use a set of muscles too much, you're likely to strain the tendons (soft tissues) that connect those muscles to your bones. At first, pain or swelling may come and go quickly. But if you do too much too soon, your muscles may over-tire again. The strain may cause a tendon's outer covering to swell or small fibres in the tendon to pull apart. If you keep pushing your muscles, damage to the tendons adds up and tendonitis develops.
Symptoms: Depending on what causes the stress or overuse, tendons in the back, sides, or front of your foot may hurt. At first you may feel pain only during or after a workout, such as running or an aerobics class. As tendon damage adds up, however, your foot may hurt when you walk and even while you stand still.