How Does Hyperplasia Occur? (Debate is settled) | Bodybuilding Web results
Muscle Fiber Hypertrophy vs. Hyperplasia:
Hypertrophy refers to an increase in the size of the cell while hyperplasia refers to an increase in the number of cells or fibers. A single muscle cell is usually called a fiber. ... Bodybuilders and other strength-power athletes, on the other hand, have much larger muscles (14,40).
Muscle Fiber Hypertrophy vs.
Hyperplasia:
Has the debate been settled?
Jose Antonio PhD
WHAT IS HYPERPLASIA?
Hypertrophy refers to an increase in the size of the cell while hyperplasia refers
to an increase in the number of cells or fibers. A single muscle cell is usually
called a fiber
EXERCISE-INDUCED GROWTH IN HUMANS
"So the
question that needs to be asked is not whether muscle fiber hyperplasia occurs,
but rather under what conditions does it occur. I believe the the scientific
evidence shows clearly in animals, and indirectly in humans, that fiber number
can increase. Does it occur in every situation where a muscle is enlarging? No.
But can it contribute to muscle mass increases? Yes."
HOW DOES MUCLE FIBER HYPERPLASIA OCCUR?
There are two primary mechanism in which new fibers can be formed. First, large
fibers can split into two or more smaller fibers (i.e., fiber splitting) (6,25,39).
Second satellite cells can be activated (11,16,17,43,44).
Satellite cells are myogenic stem cells which are involved in skeletal muscle
regeneration. When you injure, stretch, or severely exercise a muscle fiber,
satellite cells are activated (16,43,44). Satellite cells proliferate (i.e., undergo
mitosis or cell division) and give rise to new myoblastic cells (i.e., immature
muscle cells). These new myoblastic cells can either fuse with an existing muscle
fiber causing that fiber to get bigger (i.e., hypertrophy) or these myoblastic cells
can fuse with each other to form a new fiber (i.e., hyperplasia).
ROLE OF MUSCLE FIBER DAMAGE
There is now convincing evidence which has shown the importance of eccentric
contractions in producing muscle hypertrophy (15,24,45,46). It is known that
eccentric contractions produces greater injury than concentric or isometric
contractions. We also know that if you can induce muscle fiber injury, satellite
cells are activated. Both animal and human studies point to the superiority of
eccentric contractions in increasing muscle mass (24,45,46). However, in the real
world, we don't do pure eccentric, concentric, or isometric contractions. We do a
combination of all three. So the main thing to keep in mind when performing an
exercise is to allow a controlled descent of the weight being lifted. And on
occasion, one could have his/her training partner load more weight than can be
lifted concentrically and spot him/her while he/she performs a pure eccentric
contraction. This will really put your muscle fibers under a great deal of tension
causing microtears and severe delayed-onset muscle soreness. But you need
that damage to induce growth. Thus, the repeated process of injuring your fibers
(via weight training) followed by a recuperation or regeneration may result in an
overcompensation of protein synthesis resulting in a net anabolic effect (12,31).
HAS THE DEBATE BEEN SETTLED?
In my scientific opinion, this issue has already been settled. Muscle fiber
hyperplasia can contribute to whole muscle hypertrophy. There is human as well
as rat, cat, and bird data which support this proposition (1-3,5-8,13,17,20-
22,25,29,35,37,47), a veritable wild kingdom of evidence. Does muscle fiber
hyperplasia occur under all circumstances? No. There are several studies which
show no change in fiber number despite significant increases in muscle mass
(4,18,19,23,26,30,36,41). Is it possible that certain muscles can increase fiber
number more so than o
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