When you picture different athletes – marathon runners, gymnasts and Olympic weightlifters, for example – you likely categorise them instinctively by their height, size and build. But what makes these ...

Tsukuba, Japan—Muscle fibers, which constitute skeletal muscle, are classified into two main types: slow-twitch (Type I, red muscle) and fast-twitch (Type II, white muscle). Slow-twitch fibers are ...