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.
The second cause of side stitch is probably the most common. It's a stretching of the ligaments attached to the liver, pancreas, stomach, and intestines. These ligaments are put under stress when you walk vigorously. The bouncing action causes them to stretch, thereby causing pain.