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.
Causes and Background Information. Causes of Blood in Stool. Anal Fissure. If no diarrhea, most of these children have a small tear in the anus. This is called an anal fissure. Anal fissures usually are caused by passage of a large or hard stool. This is the cause in 90% of children with blood in the stools.