How muscle growth happens

Each muscle is made up of thousands of tiny muscle fibers. When you do body weight exercises, your muscles develop tiny tears in the fibers. When you rest, your body begins repairing your damaged muscle cells by fusing torn muscle fibers back together and laying down new proteins within each muscle cell.

Your nervous system, circulatory system and endocrine system all contribute to muscle repair and growth. The continued repair process creates bigger and stronger muscles.