Muscle Hypertrophy

Increased muscle size in resistance training has been attributed to hypertrophy of existing muscle fibers. This increase in cross-sectional area of existing muscle fibers is due to:

• the increased size and number of actin and myosin filaments, and
• the addition of sarcomeres within existing muscle fibers.

Not all muscle fibers undergo the same amount of enlargement; the amount of enlargement depends on the type of muscle fiber and the pattern of recruitment.

A second statement of the term (page 464, 168): hypertrophy refers to the increase in muscle size that occurs with long-term resistance training, due to an increased size of existing individual muscle fibers.

• Hypertrophy = enlargement of existing muscle fibers (increased cross-sectional area).
• Caused by increased size and number of actin and myosin filaments + added sarcomeres.
• Amount of enlargement depends on fiber type and recruitment pattern.
• Develops with long-term resistance training.

• muscle-hyperplasia — increase in fiber number (contrast; possibly 5–10%).
• muscle-atrophy — the opposite (wasting from disuse).
• muscle-fiber-types — fiber type affects degree of enlargement.
• motor-unit-recruitment — recruitment pattern affects enlargement.
• repetition-maximum — 8–12 RM (hypertrophy) on the RM continuum.