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.
Causes of Blood in Stool. 1  Anal Fissure. If no diarrhea, most of these children have a small tear in the anus. 2  Strep Skin Infection. A Strep skin infection around the anus can also cause blood-streaked stools. 3  Bacterial Diarrhea. If also has bloody diarrhea, a gut bacterial infection may be the cause.  Red, but not Blood.
Green: 1  Green stools are always normal, but they can be mistaken for black stools. 2  Bile. Most dark green stools are caused by bile. 3  Green stools are more common in formula fed than breastfed infants. It can be normal with both.  Green stools are more common with diarrhea. This is due to a fast transit time through the gut.