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.
2. Black or tarry stools (Melena) - the passage of black, tarry and foul-smelling stools; can be an indication of digested blood in the stool. Other causes are, iron deficiency anemia, cirrhosis, colorectal cancer, disseminated intravascular coagulation, peptic ulcer, or stomach cancer.