Concentric contractions: A concentric contraction is a type of muscle contraction where the length of the muscles shorten while undergoing tension. For example, when you pick up a curl bar and perform a biceps curl, the length of your biceps muscles shorten.
Here are just a few reasons why your baby may have blood in his stool: 1  An anal fissure, which is a small anal tear often caused by passing a hard stool. 2  A food allergy. 3  Maternal blood from delivery or from cracked, sore nipples.  An intestinal 1  infection. An intestinal disorder, such as colitis or intussusception.
Common Causes of Blood in the Stool. 1. Hemorrhoids: One of the most common causes of blood in the stool is that it is the result of a hemorrhoid that has started to bleed. Hemorrhoids appear when blood vessels in the rectum or anus become swollen and inflamed. Bleeding from a hemorrhoid is typically bright red in color.