What does muscle hypertrophy refer to?

Muscle hypertrophy specifically refers to the increase in the size of skeletal muscle fibers, which occurs as a result of resistance training and other forms of consistent physical activity that challenge the muscles. This physiological process involves the synthesis of new proteins and the enlargement of muscle cells, leading to more substantial muscle mass.

The other options focus on different aspects of fitness and body composition. Decreased muscle endurance involves a reduction in the muscle's ability to perform repeated actions over time, which is not linked to hypertrophy. The growth of fat tissue points to changes in body composition that do not directly relate to muscle size. Lastly, reduction in muscle flexibility pertains to the range of motion of muscles rather than their size. Thus, the notion of hypertrophy is distinctly centered on the growth of skeletal muscle fibers.