Different specific body muscles have varying proportions of muscle fiber types. Type II shorten much faster than Type 1 muscle fibers and are more often found in the upper body; most muscle groups have a more or less even mixture of both types of fiber. Generally speaking, a large volume of a type of strength fitness training produces a shift between fiber types this is potentially more detrimental to athletes who need to maintain speed and endurance. Training with lesser volumes is often seen as more beneficial to athletic trainers.