As a response to a progressive resistance training program, which of the following demonstrates the predominant contribution to an increase in cross-sectional area of a muscle?

Atrophy refers to a decrease in muscle fiber size, which is the opposite of what occurs in response to progressive resistance training.

Reversing the order by listing hyperplasia as the predominant mechanism is incorrect; hypertrophy is the primary driver of cross-sectional area increases, not hyperplasia.

Atrophy combined with hyperplasia is physiologically contradictory in the context of a progressive resistance program, as the overload stimulus produces fiber enlargement, not shrinkage.

Hypertrophy - the increase in the size of individual muscle fibers through accretion of myofibrils, contractile proteins, and connective tissue - is the well-established primary mechanism driving gains in cross-sectional area with progressive resistance training. Hyperplasia, the actual increase in fiber number, has been documented in animal models and is debated in humans, making it a possible but not predominant contributor. Placing hypertrophy first and hyperplasia as secondary correctly reflects the scientific consensus.