Muscles are comprised of fibers that stretch and tear during exercise. According to scientists at the University of Texas Southwestern Medical Center, increases in muscle mass can be attributed to muscle hyperplasia. Hyperplasia is the splitting of cells which contributes to muscle growth. This is different from the increasing of the individual cells, as happens with muscle hypertrophy.
Hyperplasia in Humans
Muscle cell splitting, as seen in users of growth-enhancement drugs, or steroids, produces damage to the muscle fibers, requiring new muscle fibers to grow and replace the defunct ones. Hyperplasia is also seen in pregnant women’s abdominal muscles, due to the rapid increase in size.
Increased Muscular Demand
Increased demand to a muscular region, due to weight lifting, may induce hyperplasia, though it is not well documented in humans. It has long been accepted that increased demand will require hypertrophic conditions, in which muscle cells increase in diameter, causing the increase in muscular size. According to Wesley James of Muscle Mass Magazine, most scientists and researchers claim that the number of fibers a person is born with are the maximum number of fibers that a person can have for life.
In the early 1980s, scientists Tesch and Larrson conducted a study examining the size of muscular fibers of a variety of exercisers. The studies, through muscle fiber biopsy, proved that power-lifters – who use low reps and high weight – had the largest muscle fibers. This is a result of hypertrophy, or a change in cell size. The bodybuilders – who use higher reps and lower weight – had smaller fibers, but more of them, contributing to their equally large muscle size.
James suggests the use of both hypertrophic and hyperplastic phases to combine muscular building in both size and strength, as well as number of fibers. Careful planning will induce strengthening of old and new fibers for superior muscle density. James, and others who believe in training for hypertrophy, advocate embarking on a hypertrophic phase, where three sets of eight repetitions with enough weight to reach failure is used for the strength building phase. In this hypertrophic phase, athletes should, according to James, increase weight with each workout for each body part.
The hyperplastic phase consists of three to eight sets of lower weight and additional repetitions, producing new muscle fibers. Unfortunately, success of hyperplasia is difficult to assess, though measuring glucosamine levels, or development of visible muscle striations will guarantee that hyperplasia has taken place.
Some of the most significant studies on hyperplasia took place in the late 1970s, completed by Dr. William Gonyea. The experiments were performed on cats that had weights attached to their limbs. The argument is the structure of human vs. animal muscle fibers, where humans have a maximum of five types of fibers and where cats can have up to 11. Gonyea's studies are highly questioned and disputed. Human studies are difficult as they require biopsies of the muscle tissue to assess the growth of additional fibers, which is why there's a lack of scientific evidence supporting the hyperplasia theory.