Does muscle hyperplasia (increased muscle number cells) occur following resistance training in humans? Probably not. 

Data suggests that when an average muscle area is divided by the average muscle fibre area (taken from muscle biopsy), the cross-sectional area of muscle is more related to the are of the muscle fibres than the muscle fibre size (MacDougall 1984). However, it is interesting to note that the subjects in this and other studies have noted that the subjects with the largest muscles also have the largest number of muscle fibres.

Interestingly, one study involved a resistance training programme for cats found a 9% difference in muscle fibre numbers in the trained v untrained muscles (Gonyea et al. 1986).