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 stool include: 1  Hemorrhoids. 2  Anal Fissure. 3  Colon Polyps. 4  Proctitis. Colitis.  Rectal 1  ulcers. Colon or Rectal Cancer.