Answer:
The human skeletal system, and the muscles themselves, are the ones responsible for movement, warmth, metabolism, posture, and other things.
Our muscles are long stretches of fibers composed by sarcomeres that form our skeletal muscle system. Each of these fibers are joined together into fascicles, and each of them are characterized by the fact that they can either be of a fast twitching capacity (FT), or a slow twitching capacity (ST). As such, according to research, human beings have in their muscles two major types of fibers, the ST, which when looked histologically are stained red, and the FT, further subdivided into FTa and FTb, depending on their metabolic response, and which usually show white or pale on the microscope.
In regards to muscle performance, these three types of fibers, and their presence in the skeletal muscle system of a person will ensure the better, or lack of good, muscle performance when in exercise. Usually, under certain circumstances, por example, exercise, a person who has muscle training, will show a higher volume of ST fibers, and will have lesser exposure to muscle fatigue, which will make them more fit to longer extensions of exercise exposure. Whereas people with lesser training will present more incidence of FT fibers, especially those that work better under anaerobic conditions. These people, when exposed to exercise, will have faster muscle responses, but, fatigue will set in much faster too, because the aerobic process takes longer to set in, as the muscles are not trained.
