Which statement correctly distinguishes hypertrophy from hyperplasia in skeletal muscle adaptation?

Which statement correctly distinguishes hypertrophy from hyperplasia in skeletal muscle adaptation?

• A. Hyperplasia is enlargement of existing fibers; hypertrophy increases fiber number.
• B. Hypertrophy is enlargement of existing fibers; hyperplasia increases fiber number.
• C. Both hypertrophy and hyperplasia refer to fiber size increases.
• D. Hypertrophy involves increased capillary density.

Answer: (D)

The key idea is how skeletal muscle adapts by making existing fibers larger versus creating more fibers. Hypertrophy means the muscle fibers themselves get bigger, with more myofibrils and contractile proteins, so the cross-sectional area of each fiber increases. Hyperplasia, on the other hand, would be an increase in the number of muscle fibers. In humans, the typical adaptation from training is hypertrophy, with limited evidence for true hyperplasia.

The statement that hypertrophy involves increased capillary density isn’t the defining difference between these two processes. Capillary density can rise with various training programs to improve blood supply, but that vascular change is a separate adaptation and not what distinguishes hypertrophy from hyperplasia. So while hypertrophy can occur alongside angiogenesis, the hallmark distinction remains: hypertrophy = enlargement of existing fibers; hyperplasia = increase in fiber number.