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.
Muscle fibers that contract rapidly are known as fast-twitch fibers. Fast-twitch fibers activate and deactivate rapidly and come in two types: Type 2A muscle fibers which fatigue at an intermediate rate, and Type 2B muscle fibers which fatigue rapidly.