The final shape of the muscle depends on genetics, followed by exercise.
1. The maximum number of muscle fibers (muscle fibers have been fixed)
Since you were an infant, you have all of your adult muscle fibers. They grow up with you and will continue to grow as you grow older if you get adequate exercise. Conversely, without proper exercise, muscle fibers can shrink and even disappear entirely. However, it is generally believed that the total number of muscle fibers will not increase.
2. The ratio of fast muscle fibers to slow muscle fibers
There is no mutual conversion between fast muscle fibers and slow muscle fibers. Since the total number of muscle fibers in the human body is determined innately, so is the athletic advantage of everyone. Whether you are more suitable for endurance or power and explosive exercise depends on which muscle fibers are more in your body.
3. Muscle shape after full exercise
There is a view that muscles can exercise the full potential of genes through exercise. The opposite view is that muscles can only be plasticized. This is the topic for the next discussion. Before that, we still thought that the final shape of the tissue depends on genetic factors first, and secondly, on the day after tomorrow.