Nephritis is the most common cause of blood in the urine of children and young adults but it can occur at any age. If your GP suspects nephritis he will usually refer you to a nephrologist (kidney doctor).
Muscle fiber types can be broken down into two main types: slow twitch (Type I) muscle fibers and fast twitch (Type II) muscle fibers. These fast twitch fibers can be further categorized into Type IIa and Type IIb fibers, which are also known as fast twitch oxidative and fast twitch glycolytic, respectively.
Type IIB (Type 2B) Muscle Fibers. Type IIB fibers, also called fast twitch or fast glycolytic (anaerobic) fibers, contain a low amount of myoglobin, mitochondria, and capillaries so they are white in color. Type IIB fibers create ATP at a slow rate through anaerobic metabolism but split it at a very fast rate.