By Greg Rose
Titleist Performance Institute

In order to increase your muscle mass you need to understand how muscles grow.  Muscles grow using either hypertrophy or hyperplasia. Hypertrophy causes the size of the muscle to increase due to an increase in the size of each muscle fiber, while hyperplasia is an increase in the number of muscle fibers.

Hypertrophy (muscle fiber growth) can occur in two ways, sarcomere hypertrophy or sarcoplasmic hypertrophy.  Sarcomere hypertrophy is when the contractile portion of the muscle actually gets bigger, while sarcoplasmic hypertrophy is when the non-contractile portion of the muscle increases in size. Sarcomere hypertrophy doesn't increase the size of the muscle as much as sarcoplasmic hypertrophy, but the density of the muscle increases. Sarcoplasmic hypertrophy does the complete opposite, the muscle increases in size but density decreases. All hypertrophy will involve both processes; the ratio is dependent on training intensity and frequency. If you are interested in improving performance, than strive for sarcomere hypertrophy. Sarcoplasmic hypertrophy is only beneficial if an increase in body weight is more important than an improvement in performance.

Hyperplasia refers to an increase in the number of cells or fibers.  There has been a lot of controversy concerning the reality of hyperplasia.  In other words, the scientific community for a long time has debated whether hyperplasia actually occurs.  It is my opinion, that hyperplasia is a reality but the majority of muscle mass gains for most of the population will be due to hypertrophy. 

According to Dr. Jose Antonio, PhD (who wrote a great article on Muscle Fiber Hypertrophy vs. Hyperplasia: Has the debate been settled?) There are two primary mechanisms in which new fibers can be formed. First, large fibers can split into two or more smaller fibers - called fiber splitting.  Secondly, satellite cells can be activated.  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. Satellite cells proliferate 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).

Regardless of how all your muscles get bigger, the question is how do we get our muscles bigger and stronger.  There is now convincing evidence which has shown the importance of eccentric contractions in producing muscle hypertrophy.  It is known that eccentric contractions produce greater injury than concentric or isometric contractions. We also know that if you can induce muscle fiber injury, satellite cells are activated. 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.

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