What does hypertrophy refer to in the context of muscle development?

Hypertrophy refers specifically to the increase in the size of muscle tissue as a response to resistance training or other forms of stimulus. This process occurs when the muscle fibers undergo stress that causes micro-tears, leading to the repair and growth of those fibers, ultimately resulting in larger muscles. This increase in size is typically sought after by individuals who engage in strength training, as it contributes to improved strength and physical appearance.

While the other options touch on different aspects of muscle physiology, they do not accurately define hypertrophy. For example, a decrease in muscle size is referred to as atrophy, which is the opposite of hypertrophy. Increasing flexibility relates more to the elasticity of muscles and connective tissues rather than the size of muscle fibers. Similarly, the reduction of muscle fatigue pertains to endurance and recovery, which are influenced by various factors, but not directly by the process of hypertrophy itself. Therefore, the option that correctly identifies hypertrophy is the increase in size of muscle tissue.