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.
Anal Tears (Fissures): Often, small tears in the lining of the anus can cause blood in the babyâs stool. The anal tissues are extremely delicate, especially in the case of a baby, and contain many small blood vessels. Sometimes, passing a hard stool could cause these tissues to tear, leading to blood in the stool.