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.
Infants might have green stool as a result of: 1  Not finishing nursing entirely on one side, thus missing some of the high-fat content breast milk, which affects the digestion of the milk. 2  Protein hydrolysate formula (for babies with milk or soy allergy). 3  Lack of normal intestinal bacteria in breast-fed infants.