The steroids put on muscle mass. I'm not sure the skeleton is going to bulk up. It does naturally to some extent with exercise, thats why they gallop horses. But if a guy is taking steroids and working to build up muscle mass his genetic skeletal system may not be up to the extra bulk and torque. A light backpack can give you back spasms if you carry it all day. Women with large breasts can have back problems as well.