wikipepedia has this:
"Muscle hypertrophy involves an increase in size of skeletal muscle through an increase in the size of its component cells. Hypertrophy can be broken down into two types of categories: myofibril and sarcoplasmic. Each of these specific types of muscle hypertrophy will result in increasing size of cells, but not of equal effect. Sarcoplasmic hypertrophy is focused on increasing the actual size of the muscle, and less on increasing strength. Myofibril hypertrophy will focus more on strength increase and less on an increase in the size of the skeletal muscle."
"Strength training typically produces a combination of the two different types of hypertrophy: contraction against 80 to 90% of the one repetition maximum for 2-6 repetitions (reps) causes myofibrillated hypertrophy to dominate (as in powerlifters, Olympic lifters and strength athletes), while several repetitions (generally 8 - 12 for bodybuilding or 12 or more for muscular endurance) against a sub-maximal load facilitates mainly sarcoplasmic hypertrophy (professional bodybuilders and endurance athletes"