Final answer:
The source of the additional myonuclei associated with muscle hypertrophy induced by resistance training is satellite cells, which donate their nuclei to existing muscle fibers during muscle growth or repair.
Step-by-step explanation:
Research on resistance training induced muscle hypertrophy suggests that cellular adaptations are key to the enlargement of skeletal muscle tissues. When we engage in resistance training, the muscles experience hypertrophy not by generating new muscle fibers, but by adding structural proteins to existing ones. This process increases the size of the muscle fibers, specifically the myofibrils within those fibers, and leads to an increase in myonuclei. The source of these additional myonuclei is satellite cells. These cells are located on the outer surface of muscle fibers and become activated during muscle growth or repair. Upon activation, satellite cells donate their nuclei to the existing muscle fibers, providing the additional myonuclei necessary for supporting the larger cellular structure and accommodating the increased production of structural proteins required for muscle hypertrophy.