Not to worry too much about terminology CAdad, but the word cell and fiber can be interchangeable when talking about muscle histology, so technically new muscle fibers/myocytes are laid down constantly in an athlete that performs enough strength training to damage muscle tissue. These new muscle cells come from skeletal muscle satellite cells( a form of stem cell). Here is an exerpt from the International Journal of Biochemical Cell Biology that may explain the concept a bit:
Muscle satellite cells.
"These act as a reserve population of cells, able to proliferate in response to injury and give rise to regenerated muscle and to more satellite cells. Satellite cell-derived muscle precursor cells may be used to repair and regenerate damaged or myopathic skeletal muscle."
I know this isn't a post on physiology or performance enhancing supplements, but this is the primary reason that I recommend the supplement HMB to any athlete over 16 that is on a strength program, studies have shown that it minimizes muscle breakdown without slowing muscle fiber regeneration and development. Studies show an increase of 6 pounds lean muscle mass over control subjects within a matter of weeks. Very neat productwithout the side effects of Creatine. But I must add that I also never recommend anything without consulting your physician first.
Sorry to go on, just trying to explain my stance on this area.