A study published over 25 years ago compared the muscle fibers of experienced, competitive bodybuilders to untrained college students. The natural hypothesis of the study authors was that the bodybuilders, some of whom had over 20-inch arms, would show much larger muscle fibers compared to the untrained students. But when the muscle fibers of the bodybuilders were compared under the microscope to the college students, the muscle fibers appeared to be the same size. This observation befuddled the scientists, who had no ready explanation for the finding. How could bodybuilders, with obviously much larger muscles, show the same-sized muscle fibers as untrained students? In the minds of the researchers who conducted the study, there was only one rational explanation. The bodybuilders' muscle fibers had undergone hyperplasia. What that meant was that the muscle fibers in the bodybuilders had split to form new muscle fibers, and as such although the bodybuilders' muscle fibers didn't appear larger when compared to the students, the bodybuilders had far more muscle fibers, and that must have explained their significantly greater muscle size.
But there was a problem with this deduction. For one, the actual number of muscle fibers in the bodybuilders wasn't counted, so the idea that they had many more muscle fibers was merely a theory to explain their muscle mass in relation to the students.Another problem was that little or no evidence existed in humans that muscle hyperplasia occurs. The accepted explanation for muscular hypertrophy or growth was that it occurred when muscle fibers were damaged, such as during exercise, and that the body compensated for this through increased muscle protein synthesis and also activation of muscle stem cells called satellite cells. When muscle fibers are damaged, normally quiescent satellite cells are recruited under the influence of anabolic hormones, including testosterone and insulin-like growth factor-1 (IGF-1). The satellite cells contribute new muscle cells or myonuclei to the damaged fibers, which leads to a thickening of the fibers. It's that increase in the cross-section or diameter of the existing muscle fibers that make the muscles appear larger. That is the accepted scientific explanation of how muscles grow.
Yet, the bodybuilders in the study showed muscle fibers that didn't appear to be any thicker than the untrained college students. In short, the accepted idea of how muscles grow didn't appear to be relevant. The only possible explanation for the bodybuilders' greater muscle size had to be that they had undergone hyperplasia. But if this was true, what caused such an extensive display of muscle fiber hyperplasia as was evident in the bodybuilders? If this effect could be explained, others who seek greater muscle mass could apply the same techniques.
Although hyperplasia in human muscle remains controversial, it does occur in some tissues and organs in the body. For example, breast tissue in human lactating mothers undergoes hyperplasia to accommodate . . .