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.
Other conditions and situations that can cause blood in the stools include: 1  colon cancer. 2  non-cancerous growths, such as polyps. 3  intestinal infections (bacterial enterocolitis) that can be caused by foodborne pathogens, such as salmonella and E. coli.  inflammatory bowel disease (Crohn's disease, ulcerative colitis)