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.
How Type I & Type II Muscle Fibers Are Different. Type I fibers are different than type IIb fibers for many reasons. You can think of them as opposites. Type I is for long endurance activities while type IIb is for short fast bursts. Type I fibers are highly oxidative and are not likely to hypertrophy as much.