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 II muscle fibers, also called fast-twitch, are large muscle fibers used for lifting heavy loads. A weight lifter has an abundance of type II muscle fibers. Competitive sprinters also have plenty of type II muscle fibers in their large leg muscles, which are used to produce strong movements for a short time.