^Although I would love to see a girl with 50k boobs, because that size would be fascinating from multiple aspects, the weight of such would be near impossible to manage without some accepted light weight filler. In any case, even working with lesser weights, while the back is important for average standing and bending, there will be a natural tendency to stand not just upright, but with your shoulders considerably back in the **61** effort to center your boobs and upper body weight over your hips. This requires well developed abdominal muscles, not to be confused with a six pack, because their development will be the result of being stretched while holding the weight in place. Still, expect to experience limited endurance in walking or any nominal exercise and the increasing need to sit and rest. And I cannot stress the need for well developed thighs, which I think Martina already has a tendency towards, because with increased size and weight comes the need for more squatting as opposed to bending at the waist, again, the desire to keep the weight balanced over the hips.
I have read about a girl with gigantomastia having in excess of 120 lbs. of boobs, or in other words, about 55k implants. The difference here is balance; there is a huge difference between a girl having most of her boob mass in front of her hips/thighs and the implant girl that hopefully would choose huge round fake boobs on her chest. Everything about her huge round globes creates more challenges, from balance to their always being in the way to obstructing vision to her ability to simply reach over them because the sideboob width has already eliminated the possibility to reach around them and prevents the arms from moving forward entirely without raising them over the sideboobs. No doubt, watching a girl manage life with boobs that size would be fascinating.
But the standout attribute has to be a absolute love for your huge boobs, so complete that you would not just tolerate all the challenges, but embrace them as constant affirmation of your size. Before you even reach 20k, absolutely nothing in your life will not be affected by your boobs size. How many 3000cc girls have we seen eventually downsize because they found their boobs were always in the way? You cannot have that attitude, but love the way they are always in your way and happily give up those things that huge boobs will make it impossible to do, while looking forward to giving up the things now difficult when your boobs get even larger. It is a fantastic dedication and love that accomplishes this, nothing less.