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.
Occult blood in the stool has many of the same causes as rectal bleeding, and may be associated with the same symptoms as more active bleeding. For example, slow bleeding from ulcers, colon polyps, or cancers can cause small amounts of blood to mix and be lost within the stool.