Inner Side of the Foot
Injuries that cause pain on the inner side of the foot include damage and strain to an important tendon called the posterior tibial tendon that helps to resist excessive foot pronation, as well as compression to a large nerve that runs through an area called the tarsal tunnel, found just below and beyond the ankle bone. Called tarsal tunnel syndrome, this compression can lead to numbness, burning, and tingling to the inner side of the foot, or the bottom of the foot.
Outer Side of the Foot
The outside of the foot is home to the peroneal tendons, which help rotate the foot outward. They can be damaged or strained when running, especially if on uneven ground. People who have flat feet that overpronate can also have excessive compression of the foot towards the outer ankle, eventually leading to inflammation in the front of the ankle joint or within a joint below it in an area called the sinus tarsi. Ankle sprains, even minor ones, can be a source of pain during running even if there is no pain when walking. The ligaments that bind the outer ankle together can be stretched or torn during a sprain injury, leading to pain and instability that can worsen during a run.