hyperplasia. Hypertrophy is an increase in the actual size of the individual muscle fibers while
hyperplasia refers to an increase in the total number of muscle fibers (1). While hyperplasia has
been repeatedly documented in animals, it is not believed to contribute to human muscle growth
to a significant degree (13-15). If hyperplasia were to occur in humans, it would be most likely to
occur with heavy eccentric loading and slow movement speeds (13).
Timing for central versus peripheral adaptations
The time course for the different adaptations to strength training has been studied using a
variety of testing protocols. During the first four to eight weeks of training, there typically is an
increase in MVIC without an increase muscle size. This implies that the majority of changes
during this time period are occurring due to the neural adaptations outlined above (6,11,16-18).
In beginning trainees, increases in muscle size do not begin to occur during the first 4-5
week (12,19) and may contribute to further increases in strength for several years. Eventually
the muscles reach a genetic upper limit in terms of strength and size which can only be
surpassed with the use of growth enhancing drugs (20). Once muscle size has reached this limit,
further increases in strength can occur due to improved technique and further neural adaptation
(1).
Beginning weight trainers should not expect to see increases in muscle size until the fourth
or fifth week of training. Although strength is increasing, the improvements are mainly in the
nervous system and simply reflect ‘learning’ how to lift weights (6,21). Some beginners are
unable to recruit the largest Type II muscle fibers which may explain the delay in growth.
(1,6,22).
Differences between bodybuilders vs. powerlifters
As stated above, some training authorities have suggested that neural factors and muscle
CSA can be developed differentially (23-25). Although little research appears to have directly
examined this assumption, we may be able to gain insight from comparisons of the adaptations
seen in elite powerlifters and bodybuilders. Powerlifters typically train with low reps often
considered the ‘neural’ training zone ; while bodybuilders typically train with higher reps, often
considered the ‘growth’ zone. Please note that it is impossible to know for certain if the following
adaptations are a result of the type of training done or individual genetics. The major differences
between powerlifters and bodybuilders appears in table 1. With the exception of total number of
muscle fibers, all of the characteristics listed have been shown to change with training.
Overall, it appears that bodybuilding training has the effect of increasing muscular
endurance (i.e. capillary density and mitochondrial density) probably due to the higher levels of
lactic acid produced with a program of high volume and short rest periods. In essence, typical
bodybuilding programs are similar to interval training in terms of the adaptations seen. It has
been suggested that bodybuilding training preferentially cause sarcoplasmic hypertrophy, which
is growth of non-contractile components such as mitochondria and capillaries, while powerlifting
training causes the actual muscle fiber growth (3,23,24,33).