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.
The ingestion of black licorice, lead, Pepto-Bismol, or blueberries can. all cause black stools or false melena. Stools should be tested for the presence of hidden blood. Some upper GI causes of bloody stools can also cause vomiting blood such as in peptic ulcer disease.