How does muscle hypertrophy primarily occur?

Muscle hypertrophy primarily occurs due to resistance training that causes microtears in the muscle fibers. This process is known as muscular adaptation, where the muscle fibers sustain small injuries during intense workouts. Following these microtears, the body initiates a repair process that involves the activation of satellite cells, which contribute to muscle growth by merging with the damaged fibers or creating new fibers. As these fibers repair, they typically become thicker and stronger, leading to increased muscle mass and improved performance. This physiological response is a fundamental principle in strength training and is the key driver behind muscle hypertrophy.

The other options, while they may contribute to muscle function and health, do not directly cause hypertrophy. Increased blood flow supports muscle endurance and nutrient delivery during a workout but does not lead to significant growth. Enhancing aerobic capacity focuses on improving endurance rather than the size of muscle fibers. Increased hydration is crucial for overall performance and recovery but does not itself induce muscle hypertrophy.