Shin splints are a painful problem with inflammation in the tissues along your shin bone. Also known as medial tibial stress syndrome, this is one of the more common running injuries. It develops when you suddenly increase the strain on your legs, like starting a new exercise program, increasing the duration or speed of your runs, beginning a hill running regimen, or wearing worn out shoes. When you develop this issue, your lower legs feel sore and tender. Sometimes they swell. Usually the discomfort increases when you are active and decreases when you rest. It can make it hard for you to continue running until the pain is resolved.