Tendons attach a muscle to a bone. When a tendon is overly stressed, usually due to poor biomechanics coupled with increased use, a tendon can become inflamed. A foot that overpronates does so due to too much motion between the bones of the foot, especially the first metatarsal. When the bones cannot stabilize properly, the muscles in the foot and leg try to make up the difference by working too hard for too long. Each muscle is designed to contract and relax while walking and running. Contracting for too long puts excess stress on the tendon and the sheath causing inflammation and pain. Severe trauma may cause tendon rupturing.