Simplify the following text for a Grade 15 native English-speaking person.
Original: Bodybuilders use weight training to improve their body image by developing their muscles for size , shape , and symmetry regardless of any increase in strength for competition in bodybuilding contests ; they train to maximize their muscular size and develop extremely low levels of body fat .
Simplified: Bodybuilders use weight training to develop their muscles for size , shape , and symmetry regardless of any increase in strength for competition in bodybuilding contests ; they train to maximize their muscular size and develop extremely low levels of body fat .