Hypertrophy involves changes such as an increase in actin and myosin within the myofibril and an increase in the number of myofibrils. Which description best captures this hypertrophic change?

Hypertrophy involves changes such as an increase in actin and myosin within the myofibril and an increase in the number of myofibrils. Which description best captures this hypertrophic change?

• A. Increase in cross-sectional area and myofibril content
• B. Increase in mitochondria without size change
• C. Decrease in cross-sectional area
• D. Increase in the number of muscle fibers

Answer: (A)

Hypertrophy is when a muscle fiber grows in size because it makes more contractile proteins and myofibrils within the existing fiber. As actin and myosin content increases, more sarcomeres are added in parallel, enlarging the fiber’s cross-sectional area and boosting force potential. The description that best captures this is an increase in cross-sectional area and myofibril content. Other options describe changes not characteristic of hypertrophy: more mitochondria without size increase reflects metabolic adaptations, a smaller cross-sectional area indicates atrophy, and increasing the number of muscle fibers would be hyperplasia, not hypertrophy.

Hypertrophy is when a muscle fiber grows in size because it makes more contractile proteins and myofibrils within the existing fiber. As actin and myosin content increases, more sarcomeres are added in parallel, enlarging the fiber’s cross-sectional area and boosting force potential. The description that best captures this is an increase in cross-sectional area and myofibril content. Other options describe changes not characteristic of hypertrophy: more mitochondria without size increase reflects metabolic adaptations, a smaller cross-sectional area indicates atrophy, and increasing the number of muscle fibers would be hyperplasia, not hypertrophy.