Bodybuilding is sarcoplasmic hypertrophy, whereas powerlifting/ weightlifting is myofibrilar hypertrophy.
Check out this paper that I wrote for one of my anatomy and exercise physiology classes. I've had to edit it abit as I originally posted it in another forum but it may answer some of your questions.
Type 1 (slow oxidative fibres, which account for approx. 50% of total muscle fibres) contract slowly (relatively very few fibres are stimulated at any one time, making them virtually fatigue resistent. These is the muscle type used by say marathon runners), are aerobic (use oxygen/ require you to "breath" during length of activity so as to create energy), have relatively low glycogen stores (as they generate a low amount of force at any one time during stimulation).
Type 2a (fast oxidative fibres, which account for approx. 35% of total muscle fibres) contract intermediately (faster/ more fibres contracting at one time compared to type 1s, but lesser compared to type 2bs, making them moderately fatgiue resistent. These is the muscle type used by you Steven, the armwrestler), are aerobic, and have moderate glycogen stores.
Type 2b (fast glycolytic fibres, which account for apprx. 15% of total muscle fibres) contract fast (a very large force generated at any given time as the majority of these fibres are being stimulated <fired by the nerve's axons> at one time, they fatigue very quickly, and are used in actions such as hitting or throwing a baseball, throwing a javelin/ shotputt etc.) are anaerobic (breakdown glucose without the presense of oxygen), and have high glycogen stores.
People are born with a pre-disposed number of the two different fibres. Some people may have 60% type 1 (born to be marathon runners), and some may have 60% type 2 (born powerlfters and weightlifters). You cannot change the ratio between type 1 and 2, but with proper training, you can change your type 2a and type 2b ratio. In some elite athletes, there are no type 2b muscle fibres.
That was only a part of one of my posts. Below was a response I wrote to 20 rep squats. There's alot of "science" in it which you may also find of use. You can find the original posts on the WSM forum:
"20 rep squats is a "positive double edged sword" in that, not only does in build the aerobic/ endurance capacity of the muscle (legs muscles in particular), but also causes hypertrophy and "strength".
When muscles are regularly employed in endurance activities such as running or swimming (or even 20 rep squats), it causes the capillaries (very small blood vessels), aswell as mitochondria surrounding the muscle fibres (where ATP energy is produced, also known informally as the "powerhouse" organelles/ components of the cell), to increase in number.
This alone allows for greater endurance, improved resistence to fatigue, and overall better muscle (cell) metabolism, ultimately improving strength (The most desired fitness component improvement wanted when performing 20 rep squats). Although this physiological improvement takes place in all three muscle fibre types, it is most prevalent in your type 1s (Remember my initial post where I described the different fibres in more detail). Additionally, these fibres contain more myoglobin which also improves the aerobic ability of the muscle.
Even more beneficial to the individual, is that 20 rep squats is a form of High Intensity Resistence Exercising. This form of free weights training stimulates muscle fibres to actually grow in size (individual muscle fibres are composed of thousands of units called sarcomeres or myofibrils, that when they contract either shorten or extend. Remember, as I described in the earlier post in the whey/ creatine thread in this section, more of these myofibrils in the muscle fibre allows the fibre to produce a greater force when properly stimulated by a nerve or as such, ultimately allowing for that muscle to move greater loads.).
This should not be confused with actually building more individual muscle fibres within the fascicle (fascicle is a small "bunch" of muscle fibres held together by a protective membrane cover called a perimysium, and has blood vessels/ nerves running through it. It is these "fascicles" that an actual muscle such as a bicep is composed of). Contrarily, it has been known that enlarged muscle fibres have been known to split/ tear longitudinally and continually grow as two different fibres. Unlike endurance work, where results are most predominant in type 1s, this activity mostly occurs in your type 2s.
Ultimately, larger muscle fibres within the fascicles within the muscle (e.g. Vastus Medialis <quadricep muscle>.), when properly stimulated by the nerves, are able to generate a greater force, capable of moving greater loads isotonically, which explains why 20 rep squats increase overall strength, aswell as endurance."
- B.A.
