I hesitate to post this because I have respect for bodybuilders and I don't want to be seen as someone attacking them. However, it was recently brought up (by Prof. X) that there was no evidence that bodybuilding leads to a disproportionate increase in sarcoplasmic hypertrophy. Well, there is evidence and I thought I'd share it. Here are some excerpts from "Supertraining" by Mel Siff.
Although the existence of hyperplasia of muscle fibers may be uncertain or rare, hyperplasia of structures within the muscle fibre and cell does occur. Nikituk and Samoilov (1990) identify two types of subfibral hyperplasia.
-Sarcoplasmic hyperplasia, which involves an increase in the number of sarcoplasmic organelles.
-Myofibrillar-mitochondrial hyperplasia, which involves increase in the number of myofibrils and mitochondria.
Increase in muscle diameter is due to enlargement of individual muscle fibres by an increase in the number and size of individual myofibrils (Goldspink, 1980), accompanied by an increase in the amount of connective tissue (McDonagh & Davies, 1984), as discussed in Section 1.6. This increase in muscle protein is produced by increased protein synthesis and decreased protein degradation (Goldberg et al, 1975). Two types of muscle hypertrophy may occur:
-Sarcoplasmic Hypertrophy. In this case, the volume of non-contractile protein and semifluid plasma between the muscle fiber increases. Although the cross-sectional area of the muscle increases, the density of muscle fibres per unit area decreases and there is no corresponding increases in muscle strength.
-Sarcomere Hypertrophy. Here there is an increase in the size and number of the sarcomeres which comprise the myofibrils. These may be added in series of parallel with the existing myofibrils, although only the parallel growth will contribute to an increases ability to produce muscle tension. The area density of myofibrils increases and there is a significantly greater ability to exert muscular strength.
So yes, there are two different types of hypertrophy. Now for the next short section...
The data shows that the longer and more strenuous the submaximal loading, the less there is sarcomere hypertophy and the more there is sarcoplasmic hypertophy.
Moderate intensity, high repetition resistance exercise, as commonly used in bodybuilding and circuit training, can also convert fast-twitch fibers to behave more like slow-twitch fibers, apparently in an adaptive attempt to resist the fatigue of the repeated efforts (Timson et al, 1985; Baldwin et al 1992; Noble & Pettigrew, 1989).
Again, I'm not trying to attack bodybuilding. I just throught I'd share that.