For Michelet, the Renaissance was more a development in science than in art and culture. He asserted that it spanned the period from Columbus to Copernicus to Galileo; that is, from the end of the 15th century to the middle of the 17th century.
Other researchers believe that side stitches are caused by stretching the ligaments that extend from the diaphragm to the liver. When a runner or walker pounds the surface while breathing in and out, he or she stretches these ligaments, and that causes the pain.
Overuse injuries are caused by repeated, microscopic injuries to a part of the body. Many long distance runners experience overuse injuries even after years of running. For road runners, the surface is hard and sometimes uneven, and the running movements are repetitive.