In reality there is glutes workout, and no heaps of workload would harm your butt. If you overdo it you'll get huge hips and ankles, that's all.
At the same time there is very little you can do on boobs front. There are exercises for granting better shape to the same volume but you have to be cautious even with those. As one my coworker puts it - "you'll deflate if you overdo it and it will be much harder to inflate you back" :(
So i started worrying about boobs well-being in a fantasy! What if your character overinflates - and discovers next time her boobs can't stretch as much? Then no inflatee is safe, not even inflatible super-heroines! Inflate too big - and you'd become deflatee, with smaller and smaller boobs in every inflation?
What do you think? Do fantasy boobs and fantasy ass react to a fantasy stretch in the startling opposite ways, like they do in reality?
Or are fantasy boobs safe?