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.

Most people won't build much muscle from traditional cardio such as walking or jogging.

But cardio that involves high-intensity exercises like plyometrics or high-volume weight training can help you build muscle to an extend. Beginners can build some muscle with hiking, skiing, and other o...