Muscle hypertrophy refers to the increase in the size of muscle fibers, resulting from resistance training or weightlifting. This process occurs when the muscles are subjected to stress, leading to microscopic damage. The body repairs this damage by fusing muscle fibers together, which increases their thickness and overall size. There are two main types of muscle hypertrophy: myofibrillar and sarcoplasmic. Myofibrillar hypertrophy focuses on increasing the density of muscle fibers, enhancing strength, while sarcoplasmic hypertrophy increases the volume of the fluid and energy sources within the muscle. Both types contribute to improved athletic performance and physical appearance.