The factors of body muscle growth of girls are lower than those of boys. As long as you don't deliberately increase protein's intake, you won't grow arm muscles. Pay attention to relax after exercise and do more butterfly chest expander 1-2 pieces. Every movement cannot be touched by the iron plate of the instrument. Finally, jumping and bathing will only make your skin elastic. You should practice your shoulders and back more. Only when the back muscles are tightened will the shoulders be closed and the chest be lifted. Come on!