What is an increase in the diameter of muscle fibers owing to the production of more myofibrils mitochondria sarcoplasmic reticulum and so forth?

Answer 1

Muscular Hypertrophy is the increase in muscle size due to increased number of myofibrils et al.

Each muscle fiber (myocyte syncytium) consists of a cell membrane (sarcolemma) containing myofilaments actin and myosin arranged in end to end segments called sarcomeres. Muscle fibers are produced by fusion of multiple myoblasts during development, with the end result being a multinucleated syncytial cell which begins to produce myofilaments.

Muscle growth occurs by production of additional myofilaments within each muscle fiber, the process called cellular hypertrophy. This results in enlargement of the whole muscle, also called hypertrophy. The number of myocytes remains the same.

Existing myocytes can be repaired during regeneration following a severe injury. Satellite cells immediately adjacent to each muscle fiber proliferate and grow, fusing to eachother and existing damaged myofibers. Severe damage also results in fibrosis, or replacement of myofibers with stiff connective tissue, and results in impaired movement. In any case the number of muscle fibers remains the same.

Answer 2

Muscle Hypertrophy.