Karin placed her weights down on the floor. She rubbed her shoulder slightly, observing the room of the gym. She sat on an exercise chair, in the very center. Only a handful of other customers of mixed genders were present. In front of her, the giant wall mirror reflected back the room to her. Karin looked at herself: wearing a black top and short, she looked out of place. Her body was an overgrown mass of muscles. She smiled, thinking that this should pay off again. Karin stood up for a moment, put her left hand on her right bicep and flexed. She contracted her pectorals, looking at the fibers of her top scream in terror, the fabric stretched immeasurably as her thick breasts became pushed by the underlying muscle. At 188 centimeters, she towered over everyone else currently present. Karin flexed her thighs, which again tested the very limits of her skin-tight shorts.
“Hmm. I’ll have to find a new pair soon,” she whispered to herself. As she picked up the weight anew to work on her arms, Karin wondered if “the thing” would happen again. There was no reason it would not, as it had happened every time she exercised in the past year. Twelve months ago, Karin measured no more than 162 centimeters and was much less muscular if still somewhat curvy and broad. More than one guy she had taken to her bed eventually told her she could gain much from exercising, that even without any workout, her body seemed made for it. Curious as she was, she eventually registered at her nearby gym and started a routine.
Karin, still thinking about the past year, was now doing a few squats, moving her waist down and up. If she had heard the slowly creeping sound of her shorts tearing near her thighs, she did not show a care. Karin stared at herself through the wall mirror, her thoughts back to that first workout she ever did. It was difficult for her to describe how energized she had felt. Every movement, every bundle of exercise she did was like a wellspring opened within her. After two sessions, she already saw visible progress. Being so inexperienced, she assumed it normal to suddenly have defined biceps after the equivalent of four hours of exercising in one week. That second week, when she took a lover home, sex had never been better. Karin ravaged him, using her legs as a vice for his head, pushing her sex against his face, she discovered a dominant streak within all the while satisfying a newfound submissiveness her lover didn’t know he possessed. It was after their second session together that he remarked she was not only more defined, but taller.
Karin’s progress was unparalleled. Her muscles grew substantially faster after every session. Sometimes, she came home from her workout, towel still around her neck, and promptly undressed in the nude, throwing her clothes away on top of her sofa, her wide living room, bathed in light through large wall windows, shining every single line of rapidly defining muscle on her body. Her body usually overflowing with hormones after a session, Karin did the usual: she laid down on her couch and started burying her fingers inside her sex. The release was powerful, potent and humid.
“I shouldn’t think about that….” thought Karin, noticing the visible growth of not just her hardening nipples, but a growing tent on the front of her short as the image of grotesquely overmuscular vaginal lips began to show. Karin relaxed from her squats and stared straight at the mirror, noticing her eyesight was now just above its highest point. She passed a finger on her top, feeling the bumps from the places it had begun to rip. Her other hand did the same for her shorts. Karin bit her lower lip softly. The other gym customers were still avoiding looking at her—A freak show—thought Karin—they must see me as a freak show—
After the first few months, the energy Karin felt filling her every time she had gone to exercise was now constant. She would wake up with it, a rampant overload of her senses which more often than not led either to masturbation, or sex, if any other man or woman was to be sharing her sheets. This morning, when Karin had awoken, it was a different matter: this rabid energy was overwhelming. She ravaged the woman she had brought home with her the night before, five times in a row. But nothing made her feel spent. She looked at her guest leaving the house, tired and apologetic for not being able to keep up, and immediately left for the gym. Karin was visibly bulging. She was already a beast from the previous months of workouts, but today it felt like she pulsed. As she walked to the gym, every step gave her the impression she was bigger, larger.
And now that she had begun, she realized something big was coming. Something she could not contain. The sound of fabric ripping audibly echoed through the room. Karin stifled a laugh, turning around to see one of her monstrously muscle-ridged glutes piercing through the short. A wetness formed on the front of her sex as excitement took her. Behind Karin, a woman gasped, shocked at the naked display.
“Hah, I’m so sorry. My body always gets a bit out of control when I pump,” apologized Karin. Her body rippled with goosebumps. She took a step towards the woman. As her right foot touched ground again, a snap passed through her body, her entire mass pulsing outward, blowing her vestments apart and exploding her sneakers in a tattered mess of rubber. The woman looking at her screamed, eliciting the gaze of all other customers. Karin had grown outward to 220 centimeters. “It’s OK! Don’t worry, I’m just a fast grower when I exercise. I’ll just go get a towel and cover up,” said Karin in a sort of oblivious way. She took one more step, and again this time as her foot touched the ground not only pulsed outward, her muscles relatively larger on her squaring frame, but also eliciting a powerful stream of girl cum out of her sex. Karin’s eyes rolled upward, her body growing to 261 centimeters, her head only a few paces away from the ceiling, her body radiating heat, a monstrous mass in the middle of the room.
Karin had an uneasy smile. She struggled to keep the energy within her. Her careful exercising of the past few months as she had found difficulty to contain the beast within was now coming out all at once. She put her hand up, trying to ease the woman’s fear, and took one more step. Her rising thigh bulged outward like a mass of dough. Her moving shoulders inflated with cords and striations of raw mass. Her neck grew out the side of her head as the muscles of her back pushed out and upward. The moment her foot landed, Karin’s body audibly groaned, not unlike a large wooden boat, before her frame shot in every direction, filling the sight of the panicked woman. Customers fled, some jumping through the window as the mass of muscularly bulging skin rushed towards them, pushing gym machinery aside.
A powerful, deep, guttural moan of pleasure blasted out of the building, strong enough to be heard up to half a kilometer away. Mixed with the advancing wall of flesh was a powerful torrent of lubricant, no doubt expelled by Karin’s orgasmic state. Outside, the gym’s walls bent outward, one of them suddenly being broken by a massively thick foot, easily six times longer than the average person.
As sudden as it started, the growth halted. Dust settled inside the ruins of the gym. The woman that had been in front of Karin was now pushed against the far wall, her body pressed between two undistinguishable muscles. Her face pushed sideways, barely able to breathe, she heard Karin speak: “I’m a bit stuck it seems, ha ha ha! Sorry about this. Maybe if I just push against this wall here…”
The stuck woman screamed at Karin: “Don’t move. DON’T EXERCISE!” It obviously fell on deaf ears. The very moment Karin’s muscles felt they had been beckoned, the valve within her body opened up anew. The woman braced herself as she felt Karin’s skin shake with goosebumps, a terrible shake growing in intensity rumbling through the barely holding walls. Dust fell, the wall behind them cracked, filled with the sound of the wooden beams usually hidden by plasters snapping from increased pressure while the noise of exploding pipes added a strange rhythmic, drumming impression, only for everything to stop.
For a moment, silence filled the air. “What….” the panicked woman questioned. A split second later, Karin’s size exploded outward. Outside the gym, nearby passersby were instantaneously overtaken as a giant upside down foot projected passed them with tremendous speed, pushing asphalt like inconsequential sand. The following thigh pulsed with growth, its mass shifting and raising the leg overall from its bulging circumference.
A nearby couple threw themselves to the ground, just in time for the growing glutes to pass overhead, missing them by a few decimeters, the wind from the speed of growth barely leaving them their clothes on from the displaced air. Like before, the raw pulse of energy subsided instantly. The hiding couple looked to their side, noticing the sky appearing again with a massive, incommensurably large striated abdominal to their side, Karin’s waist extending several stories high as she turned to her sides.
Karin rose. Her body, almost a cube now in mass, was monstrous. Her movement, slightly impeded by her strange new form, seemed still possible. She placed her foot down, trying to achieve balance, noticing it twice as large as the now-ruined gym had been. For leagues around her, people fled the area. The earth visibly buckled as the combined weight of her body created undue pressure to the soil, visibly slacking the plain the city had stood in for centuries.
“HA HA. OOPS. IT SEEMS I MIGHT HAVE OVERDONE THIS WORKOUT A BIT.” Karin was overwhelmed. Her entire frame looked as if she was flexing her muscles, every part of her striated with endless effort, but not to grow anew: Karin was trying to hold it in. She felt instinctively, at this point, that any relaxation would allow the bottled energy within her to release. Karin took a step forward, the shockwave throwing down nearby buildings, her body barely able to find its center of gravity. Karin wasn’t certain what to do. She had to hold. She had to keep the growth in.
Amidst two pulsating masses of striated muscle, atop her pectoral, the woman from the gym awoke, stuck in between Karin’s mass. She looked upward at the bulging neck of Karin, at her pained expression. She knew there would be no escape, that she was now stuck on her. Karin’s entire body now tried to break free of her will.
—This is it—thought Karin—my last workout—she could never stop trying to contain the beast within, she mused to herself. For minutes, her breathing had stopped. Karin opened her straining eyes, a wave of relaxation passing over her as she relaxed. One moment of weakness. “OOPS,” whispered Karin, her body filling with energy….
She filled the skies in an instant.