Complex sentence: The total number of skeletal muscle fibres has traditionally been thought not to change, and it is believed there are no sex or age differences in fibre distribution, however, relative fiber types vary considerably from muscle to muscle and person to person.
Split into simpler sentences: The total number of skeletal muscle fibers has traditionally been thought not to change. It is believed there are no sex or age differences in fiber distribution, however, relative fiber types vary considerably from muscle to muscle and person to person.