great question. hgh may increase the number of cells through hyperplasia; however, maintaining muscle cells - for instance - is primarily determined by the overall metabolic pathways that are engaged. if the anaerobic pathways are the primary, you may find yourself in an overall anabolic state. if the aerobic pathways are the primary, due to a chain reaction at a cellular level, your body may be in an overall catabolic state. diet plays a huge role in this as well; if your energy pathways during exercise are primarily anaerobic but you don't get the proper nutrition, guess what? catabolism takes over to deaminate proteins for glucose and glycogen synthesis. therefore, your muscle cells are broken down and no longer contribute to the roles of skeletal muscle tissue. exercise is only the stimulus; nutrition is the building blocks. +1 for such a good question