Rick stared at his reflection and flexed. The lettering around the antique mirror glowed, illuminating the young man. He grinned as the power flowed through him. It immediately began pumping up his nearly non-existent muscles with each flex. He flexed his arms. The small bicep on his arms rose a tiny bit. He switched to a leg flex causing his quads and hamstrings to bulge a little, but it was almost imperceptible.
The handsome man went through the different flexes. Arms, legs, chest, lats, traps, abs, repeat. With each flex, that body part grew just a little more. He smiled. It was working. Soon, his skinny arms began sporting lean baseball-sized biceps, his chest grew out into real pecs, his abs cobblestone block under his black treasure trail, his lats were starting to look like wings, and his legs were starting to look like tree trunks.
Rick took a moment to stop and admire his new physique. He grinned, his neck looked a little thicker, his face a little more masculine, more manly, then when he started flexing. The definition of his muscles was amazing and the feeling of growth, intoxicating. He couldn't get enough.
He went back to flexing. Each flex now more powerful than the last. As his muscles grew, so did his confidence. His flexing sped up and he started to growl with each spurt. He continued growing until he looked like a bodybuilder. Arms grew to 18" around, lean... his beefy pecs sticking out several inches in front making it hard to see beneath them, wing like lats even when relaxed, true tree trunk thighs that pushed each other apart.
He continued to grow with each flex. Each muscle inflated just a little more. Rick loved every second of this. He was getting huge. Not just muscular.... huge. His arms pushed past 20" around, his pecs bulged out ever further, blocking his view of his increasingly massive physique below. He wasn't just looking like a bodybuilder anymore, but like a bulked up superheavyweight bodybuilder. His range of motion was becoming limited, but despite that, he continued flexing. rick tried to do a back flex and check himself out in the mirror, but his traps had grown halfway up his neck and kept him from turning his head far enough to see the mirror over his shoulder.
Rick shrugged and continued flexing. His biceps were large enough now that he couldn't fully bend his elbow before his forearms met them. His chest kept his arms from meeting in front of him and met his chin if he looked down. His lats pushed his arms out at an angle even when he was relaxed. 400 pounds of muscle. At least. His abs started to bow out just due to the sheer mass of muscle that now composed them. His quads were bigger around than his waist used to be and kept him from even coming close to being able to putting his knees together. He had to again widen his stance as his thighs push against eachother. Still the growth surged. Bigger and bigger he grew. He was a monster. A freak, an impossibly large overgrown hulk that wouldn't ever be able function like a normal man in society. What clothes could fit over this extreme bulk? He had to be close to 500 pounds... and still Rick flexed in the mirror, wishing to grow even larger still. The mirror had its hold over him, and he wanted to push its limits. He wanted to be inhuman, to be overgrown, too big, too massive, to be that insanely hyper muscular.... Despite his declining mobility, he flexed again, pushing showing off arms that were getting close to 40 inches around. Only a fraction of his mass was even reflected in the mirror now... he was too big too see much of himself at all.
Rick grinned, his body absolutely, inhumanly enormous. 600 pounds, probably more. As he grew beyond the mirror's power. He couldn't move his arms any more than an inch in any direction. His abs were so bloated he couldn't bend forward and his lats, wider than a doorway, kept him from bending backwards. His traps immobilized his neck completely and his pecs were pushed up to his chin by his abs. His legs were so bloated that he had to waddle them around each other to step, but he could still only move them inches at a time. 700 pounds of insane, hyper-muscular, grotesquely overblown mass.
Rick Smiled. He was totally nude, and he'd be permanently unable to find clothes to cover his monsterous frame. "Time to go show off!" He growled before breaking down the wall on his way out.