Ben knew that he couldn't keep on growing forever, but he also loved the feeling of packing on more and more muscle. He could feel his torso lengthening in order to allow his abs to grow more. A few moments ago, he had been barely able to move, but as his body structure was changing now to accomodate the increasing amount of muscle, Ben could now start to explore his new body.
He flexed his left arm, and his beachball-sized biceps responded by swelling even more, inflating with size and power with each passing second.
Ben adjusted his stance in order to make room for his quads, which were getting bigger and bigger as well. It was a good thing that Ben's body structure kept on changing, his hips adjusting so that he could widen his stance further than any other human being. Every time he shifted his feet outwards, however, the space between his legs was quickly filled up with more muscle, so that he had to move his feet again - and again the size of his quads and calves increased.
The same, Ben realized, was happening with his upper body. His ever inflating pecs were struggling for room, pushing against each other until there wasn't even the tiniest bit of space left. Just when it seemed that they couldn't possibly grow more, Ben's rib cage expanded, releaving the pressure the two competing mounds of muscle on Ben's chest had built up in their fight. This new freedom didn't last long, though, as Ben's pecs immediately resumed their fantastic growth, blowing outwards and upwards, pressing his nipples down on his abs, already protruding about two feet from Ben's chest and showing no sign of stopping.
At the same time, Ben's lats and back muscles kept pace with his pecs, growing wider and wider, pushing his arms upwards while the growth lasted. Every time the growth subsided and Ben's rib cage expanded, there would also be more room for arm movement again. But of course this space would soon be filled up with more muscle, lats spreading like wings, further and further, wider and wider.
Ben stood in the middle of his room, afraid somehow of his unlimited ability to grow, but at the same time overwhelmed with an intense sense of power and an incredible feeling of strength. With every passing second, he added several pounds of muscle to his already unbelievably huge frame, gaining some height with the changes of his body structure, but mainly becoming broader, thicker, heavier and - above all - more and more muscular. Part of his mind told Ben to stop the growth before he got bigger than his own room, but another part wanted this to happen more than anything else.
So there Ben stood, the biggest and most muscular man of all time, trying to make up his mind what he should do next.