Chapter 11 - Section 11.6 - Muscle Metabolism - Apply What You Know - Page 423: 1

Muscle growth in adults is primarily the result of hypertrophy, not hyperplasia. Let's define these terms: 1. **Hypertrophy**: - Hypertrophy refers to the increase in the size or cross-sectional area of individual muscle fibers or cells. - In the context of muscle growth, hypertrophy occurs when existing muscle fibers increase in size due to an increase in the volume of contractile proteins, particularly actin and myosin. - Hypertrophy is the most common mechanism by which muscles grow in response to resistance training (such as weightlifting) or other forms of muscle-strengthening exercise. It involves the enlargement of existing muscle cells rather than the generation of new muscle cells. 2. **Hyperplasia**: - Hyperplasia, on the other hand, refers to the increase in the number of cells in a tissue or organ. - While hyperplasia can occur during early development and in certain tissues in the body, such as the growth of new cells in the skin, it is not a prominent mechanism for muscle growth in adult humans. - In the context of skeletal muscle, the primary mechanism for increasing muscle mass is hypertrophy of existing muscle fibers. The number of muscle fibers (muscle cell nuclei) in an individual remains relatively constant in adulthood. In summary, muscle growth in adults is predominantly achieved through hypertrophy, which involves an increase in the size of existing muscle fibers as a response to exercise and other stimuli. While some research has suggested that very limited hyperplasia may occur in response to extreme resistance training or injury, it is not considered a major contributor to muscle growth in most individuals.

Muscle growth in adults is primarily the result of hypertrophy, not hyperplasia. Let's define these terms: 1. **Hypertrophy**: - Hypertrophy refers to the increase in the size or cross-sectional area of individual muscle fibers or cells. - In the context of muscle growth, hypertrophy occurs when existing muscle fibers increase in size due to an increase in the volume of contractile proteins, particularly actin and myosin. - Hypertrophy is the most common mechanism by which muscles grow in response to resistance training (such as weightlifting) or other forms of muscle-strengthening exercise. It involves the enlargement of existing muscle cells rather than the generation of new muscle cells. 2. **Hyperplasia**: - Hyperplasia, on the other hand, refers to the increase in the number of cells in a tissue or organ. - While hyperplasia can occur during early development and in certain tissues in the body, such as the growth of new cells in the skin, it is not a prominent mechanism for muscle growth in adult humans. - In the context of skeletal muscle, the primary mechanism for increasing muscle mass is hypertrophy of existing muscle fibers. The number of muscle fibers (muscle cell nuclei) in an individual remains relatively constant in adulthood. In summary, muscle growth in adults is predominantly achieved through hypertrophy, which involves an increase in the size of existing muscle fibers as a response to exercise and other stimuli. While some research has suggested that very limited hyperplasia may occur in response to extreme resistance training or injury, it is not considered a major contributor to muscle growth in most individuals.