What is the definition of hypertrophy in muscle training?

Hypertrophy in muscle training is defined specifically as an increase in muscle size due to an increase in the cross-sectional area of the muscle fibers. This physiological response occurs primarily as a result of resistance training and involves the process of muscle fibers being subjected to stress, which leads to microtears. As these fibers repair themselves, they not only recover but also grow larger and stronger, hence increasing the overall size of the muscles.

This concept is distinct from other physical adaptations such as an increase in stamina or endurance, which pertains to the efficiency of energy systems and does not specifically involve muscle size. Furthermore, decreased muscle strength is irrelevant to the definition of hypertrophy, as hypertrophy generally contributes to increased strength. Lastly, the formation of new muscle fibers is a separate phenomenon, often referred to as hyperplasia, and is not the primary mechanism driving muscle hypertrophy.