" myofibrillar hypertrophy, more actin, myosin, and other associated proteins are added to those already existing in the cell. More contractile elements within the cell mean more actin/myosin interactions and more force production. This type of hypertrophy is typical of low-repetition, high-intensity training. It adds less mass but produces greater increases in the force generated per unit area of muscle than the second type of hypertrophy, sarcoplasmic hypertrophy. "

― Mark Rippetoe , Practical Programming for Strength Training