Which of the following best describes muscle hypertrophy?

Muscle hypertrophy is primarily characterized by an increase in the size of muscle fibers rather than an increase in the number of fibers. This physiological adaptation occurs as a result of resistance training and involves the growth of the myofibrils within the muscle fibers, leading to greater muscle mass and strength. When muscles are subjected to stress, such as lifting weights, small tears occur in the muscle fibers. The body repairs these tears by fusing muscle cells together, which increases the size of the muscle fibers as well as their number of contractile proteins.

The other options do not accurately describe muscle hypertrophy. For instance, an increase in the number of muscle fibers pertains to a different process known as hyperplasia, which is not a primary mechanism involved in the development of muscle hypertrophy. Additionally, muscle hypertrophy is associated with an increase in muscle strength, not a decrease, and while flexibility can be influenced by training, muscle hypertrophy itself does not inherently involve a decrease in flexibility.