Which of the following exercises primarily targets muscle hypertrophy?

Muscle hypertrophy, which refers to an increase in the size of muscle fibers, is primarily targeted through resistance training that focuses on higher weights with lower repetitions. This approach stimulates the muscle fibers to adapt and grow in size due to the intense loads placed upon them. The mechanism behind this involves creating micro-tears in the muscle tissue, which then heal and increase in size during the recovery process, thanks in part to the body's hormonal responses and nutrient uptake.

In contrast, high repetition with low weight focuses more on muscular endurance and may not provide the same level of mechanical tension necessary for significant hypertrophic gains. Endurance-based cardio workouts primarily enhance cardiovascular fitness rather than muscle size, while flexibility stretches are intended to improve the range of motion and flexibility rather than stimulate muscle growth. Hence, low repetition, high weight exercises are recognized as the most effective method for promoting muscle hypertrophy.