Barely under control, Logan rammed his dick into my tight ass, waves of strength rippling over his body. My muscular ass gripped Logan's dick like a vice. Logan leaned over and grabbed the sides of the desk, slamming his dick into my willing hole. I took Logan's upper arms into a tight grip, feeling the already huge muscles beginning to grow even bigger.

"Muscle, muscle, muscle," I breathed, my lust for Logan expanding with the doctor's growing body, and inspiring an equal arousal in Logan. Logan threw his head back and let out a deafening, primeval roar, searing my guts with hot cum, unable to hold back so erotic was the sensation of giving pleasure and the awesome sensation of his muscles growing larger, filling with more and more incredible mass. If anything, Logan's dick became even harder and bigger as he continued to grow and fuck his muscle buddy. I could barely believe my eyes! It was like being fucked by the Incredible Hulk! Logan reared back, never missing a stroke of his fucking, and hit a massive double biceps, his arms now pumped up to 25 inches and still expanding with hot, hard muscle. "Holy shit!" I yelled and I reached for Logan's growing cannon- ball biceps. I cupped the surging muscles, feeling them grow and expand bigger and bigger, pushing against my hands. It was the ultimate posing display! The sensation was too much, much too much! My dick, untouched, let fly, spurt after spurt of my cum covering my face and chest. Logan's assault on my ass continued relentlessly, powered by increasingly larger and larger quads that bulged obscenely against the desk, each individual massive muscle cording his thighs standing out and growing, looking like the root system of a sequoia. I moaned out encouragement, my legs around Logan's waist pulling the growing giant deeper into my fuckhole. My dick was still rock hard and I felt like I could come again and again, I was so turned on by Logan's muscles and cock. Logan dropped his arms and hit a lat spread, the muscles growing heavier and heavier. I had to stretch to reach the expanding muscles as they grew wider and wider, the slabs of awesome muscle vibrating with power and mass.

"You wanted more muscle, you got it, Mike! 75 pounds more!" Logan leaned over and kissed me. I could feel his pecs growing against mine and I pulled him down against me. I couldn't believe how heavy he was! The bulge in his guts had shrunk quite a bit but there was still an awful lot of fuel waiting to be turned into muscle. I reached around to feel the muscles on his back grow thicker. His chest and back had expanded to the point where I could barely reach all the way around!

Logan lifted his weight from my chest and grabbed the edge of the desk above and to either side my head. His two quivering, growing arms flexed beside my face and I lifted my head between the muscles. His mighty arms as big as many bodybuilder's quads squeezed my head as he lowered his weight on to me again. Logan couldn't resist the lure of his growing biceps and alternated kissing me and licking his own muscles. Struggling against the masses of muscle trapping me, I turned my head to meet Logan's lips on his bicep. Our tongues met on his bicep in a three way kiss. I felt totally surrounded and engulfed in muscle, muscle that kept growing and growing. Logan released the desk and flexed his arm which by now must be over 27 inches.

"AH FUCK!" Nearly passing out, I came again and my spasms almost knocked Logan off me. My entire body screamed with outrageous pleasure. With cum dripping from his pecs, Logan pushed himself up and stroked my brow while I gasped to catch my breath. We were both dripping wet with sweat and cum. When I could breath and see again, I could feel just how big Logan's dick had grown in my butt and see how much his muscles had expanded. Logan was trembling with the effort of keeping still and the desk began shaking violently under me.

"Pose for me, muscle stud! Fuck me with your giant dick!" He made sure I'd got my second wind then began fucking me again. I hoped the desk and my ass could take the pressure. His fucking and growing had pushed the desk 10 feet across the room to hit against a wall. Fortunately, we didn't hit any equipment. I started to jerk off and call out poses I wanted to see. "Double biceps," "Lat spread," "Most muscular."

Logan hit pose after mind-numbingly massive pose for me, his muscle shining with sweat and cum. He must have weighed close to 350 pounds of freaky muscle. His shoulders had grown and grown, each as big and as hard as a bowling ball. His pecs were twin plates of eye-popping, shredded muscle, huge square mountainous slabs pushing and growing outwards. Veins like ropes covered the muscle stallion's massive frame and even when Logan relaxed between poses, his muscles stood out as rawly defined as the anatomy chart of a demi-god.

Abandoning his posing display, Logan pulled me to his heaving chest and easily lifted me from the desk. I threw my arms around Logan's unbelievably wide shoulders, stunned at the way Logan's muscles still continued to grow and pulse against my body. Logan carried me across the room, my ass still impaled by his throbbing dick. Logan stopped with his back to a mirror and stood with his tree trunk legs planted far apart and knees bent supporting me with his now 40 inch quads. I strained to see over Logan's enormous trapezius and look into the mirror at the vast, rock-like terrain of Logan's back flaring from his tiny waist to his ever widening shoulders. I was overwhelmed with the sheer width and thickness of Logan's back. Relaxed, the muscle hung like two sides of beef beside his spine. Flexed, his back was a gut wrenching, pulsing mass of incredible contours, muscles crowding and pushing each other into fantastic prominence. Even the globes of Logan's muscular ass were thicker and ripped to the bone.

Gripping my lats securely just under my arms, Logan bounced me up and down on his dick, rippling the giant muscles of his arms and shoulders. My dick slid up and down the huge cubes Logan's washboard stomach, butting up against the huge protruding shelf of pectorals which Logan flexed, squeezing my dick between the slabs of beef and sending me into paroxysms of pleasure. Logan's bouncing became more frantic and powerful and he stood on his toes and flexed the now absolutely freaky 30 inch calves that swelled from his legs, the hugely gnarled muscles easily lifting both of us.

The masses of ripped muscle pulsing against my skin, the sight of it flexing and rippling under paper thin skin, the sheer unreal size of the muscle man fucking me was about to send me over the top again, my dick was so hard I thought it would explode. "Oh man, I'm going to cum again!" I moaned. "Flex your arm for me, muscle stud!" I threw one arm around Logan's muscle corded neck as the muscle man raised his mighty arm and flexed the absolutely huge, incredibly peaked, savagely dense 28 inch biceps. As soon as my tongue touched the insanely huge muscle, cum exploded from my dick in a mind shattering orgasm to plaster Logan's pecs with an endless stream of white spunk. Roaring inarticulately, hips spasming, Logan let loose with one final, earth shaking thrust, ramming his dick deep into my ass and shooting spurt after spurt of hot cum into my gut, every muscle on his body flexing gigantically.

After what seemed like hours, we slowed to a halt and held still, every tiny movement taxing our overextended senses. After a while, Logan stepped back against the mirror and slowly slid to the floor. We sat spent and shaking with the power of our orgasms and the power of this unprecented fuck. With bodies plastered together with the stuff of three of my orgasms, we shared a tender kiss. I lay my head on Logan's pecs and after a while his dick got too soft to stay in my ass. I sighed when that happened then turned and leaned against him. I sat between his legs and wrapped his tremendous arms around me. Practically smothered in muscle, I purred and closed my eyes.

Part Two: Mike's Turn.

"It's your turn, Mike," I awoke with a start as Logan's chest rumbled against my back when he spoke. I could hear a beeping sound coming from the growth factor machine. Once again, I was stunned at the astounding weight of Logan's muscle-laden limbs still wrapped around me.

Logan's hands cupped my pecs and he nuzzled my neck and traps. "Now, this will take a little more time. The growth factor will take a while to reach all of your muscles, so we can't start the growth fuel until it does. You wouldn't want to be lopsided would you?"

"No, I guess I can wait a bit more to catch up to you. As long as you let me play with your muscles," I replied and flexed my pecs.

"You can play with my muscles anytime, Mike." Logan stood and stretched. Man, he was practically twice as wide as me and more than 100 pounds heavier! I had never felt this small compared to another man, not even when I first started lifting. I wrapped my arms around his legs and buried my face in his crotch. I could barely reach all the way around. Logan's dick, soft now after it's recent exercise, looked as long as it was when it was hard before he fucked me and grew. I couldn't decide what I wanted now, his dick again or to start my own muscle growth.

Logan lifted me to my feet and we hugged, our bodies in contact from head to toe, our sweat and cum mixing as we rubbed our pecs against each other. There was a pop as we broke the seal created between our hard bodies and my nose was filled with the scent of sex and muscle. My dick began to get hard again.

"I'll be right back," Logan said and I could swear I felt the floor vibrate as he went to the console. His back still shone with the sweat that dripped on my face from his powerful muscle-growing fuck, highlighting every deep cut and striation of his back, ass and legs. As he bent over to get the growth factor, I got a great view of his amazing glutes, perfectly shaped and rock hard. I watched his huge muscles ripple as he worked but my gaze kept returning to those fucking striated ass muscles. My dick was completely hard again, painfully hard. Logan must have felt my eyes on his ass as he worked because he kept flexing it erotically. It took me a minute, but I got the hint, got up and let my dick lead me towards the object of my most intense fantasies.

Logan's ass flexed hard when my dick made contact with his powerful glutes. I applied more and more pressure but there was no way I could penetrate that muscular barrier without his consent. It felt as if my dick had hit a concrete wall and even sliding my dick down between his quads was impossible. Vibrations assaulted my cock and I heard a deep rumbling. What I thought was the beginning of an earthquake turned out to be Logan's laughter. I almost shot my load right there when he relaxed and straightened up, trapping my dick between his glutes. I had to grab his pumped up lats to keep from being knocked over when his thunderous back hit my pecs.

"Mmm, that feels good," rumbled Logan and he pulled my arms around his torso. I squeezed him hard and pressed my face between his oversized traps, breathing hard and on the edge of cumming yet again. Logan's massive frame writhed against mine, a fresh layer of sweat lubricating our gyrating motion. My cock caught on his asshole several times but before I could follow through and fuck the huge muscle stud, he spread his lats wide and broke my grip. I had to step back or be pushed over with the force of his back expanding.

"Why don't I give you your shot, now, big guy," said Logan turning around. There was no doubt about it, the growth factor worked on cocks as well as muscle. Logan's was as hard as mine but half again as long as my eight inches. But even a foot long dick looked small on such a massively muscular man. Logan's body literally dripped muscle and all of it seemed as hard as his cock. I stood mesmerized. Even standing still, Logan's muscles writhed and rippled with immense power, glistening with sweat and cum. I realized that I really would do anything for this muscle god. Logan twisted around and picked up what must have been the syringe but it looked like something right out of Star Trek. I gasped at the realization that my moment had come. He was about to start me growing. Bigger. As big as he was. Then even bigger.

"Relax Mike," said Logan, "Breathe." I exhaled with a grunt. I felt as if I were going to explode and I hadn't even had the shot yet. I saw that even Logan's hands had grown more muscular when he took my cock in his grip. "Remember I told you the growth factor amplifies and accelerates your own biochemistry, so it works best if I give you the shot in your balls."

I just nodded. I'd have given my left nut for the sex we had, or even half the growth he'd experienced, and I'm sure the look in my eyes said as much.

"OK. This actually won't hurt but you may lose your hardon for a bit. But once it comes back, I doubt it'll go down for hours." He cocked an eyebrow and leered at me, then bent down and pressed the strange device against my left nut. I heard a small hiss and I felt a cool sensation which evaporated as soon as he removed the space age syringe. Then he repeated the process on my right nut. He was right, even though I was on the edge of another orgasm, my dick began to get soft. It was the strangest sensation. I was on my way.

"You don't know how long I've waited to share this with someone. You're not the first to try, you know."

"I'm not?"

"No. For some reason it doesn't work nearly as well on heterosexuals, only gay men. I lost some funding when that got out. Fortunately, I found some private donors."

I let out a sigh of relief and grinned. "Shit man, in that case it's going to make me a fucking monster!" I hit a most muscular and growled at Logan.

"Mmm, just what the doctor ordered," Logan growled and mirrored my pose. Fuck he was hot! Even in comic books I had never seen anyone so big and so muscular! The pressure in my balls was growing more intense and I had completely lost my hard on. The conflicting sensations were driving me crazy. Beads of sweat appeared on my forehead, my chest and back. Even on my legs.

"It's starting to work, Mike. Come on. A cool shower will help, and I'll let you wash my back." Logan led me to the showers, walking by my side with his hands on my shoulders. Everywhere his heavy muscle contacted my skin, more and more sweat appeared. He let go of me to go in first when we got to the door to the shower room because it was way too small for the two of us to go through at once. I turned to see Logan walk through the door sideways, and even then filling the doorway. At least _his_ dick was as hard as ever. It even hit the doorframe as he passed through.

I couldn't believe the amount of sweat pouring of my body. The pool of sweat at my feet spread wider and wider. My balls felt on fire and waves of heat spread through my body. I was burning up as if I had a raging fever but I was actually starting to feel good, as if I had run 10 miles and still had the energy to do 10 more. 10 more? Hell I felt like I could run a marathon, but every move I made just made my temperature rise.

Logan brushed past me and went in and turned on the showers. My skin tingled at his touch and I went to join him. In spite of the growing heat, I felt incredible, like a panther, sleek and powerfully defined. I was becoming very conscious of my muscles. I was aware of each and every one and how much it was flexed. I checked to see if I had grown at all, but no, it looked as if I had lost weight! I flexed my arm again and it was the same size it had been before the injection. What had changed though was my skin. Not only was it noticeably thinner, but the stretch marks on my shoulder were fading and the colour was evening out, even looking a little darker in tone.

"Hey, Mike, get your skinny ass in here!" called Logan.

"If I'm skinny, it's your own fault. This shit's making me lose weight!" I had to raise my voice to be heard over the noise of the showers, and I was astonded at the volume I produced.

Logan was standing in a corner between two shower heads and had angled them both to spray his immense body. I was struck again by the sheer size of the doctor and the fact that he wanted me to get much, much bigger than his 350-plus supernatural pounds. I was mesmerized watching the torrents of water pour of his gigantic body. He flexed a 28 inch bicep against his greatly mounded pecs, rubbing the pumped muscles that rivaled each other for size. His dick was jumping up and down in time with the motions of the muscles above. His quads were astonishingly thick, almost overpowering the rest of his physique and flared almost as wide as his shoulders with massive teardrops suspended above his knees. His lower legs and even his feet were astonishingly muscular. I wanted to lay at his feet and lick his bulging calves. His eyes met mine and my knees almost buckled. He lowered a massive forearm to obscure his cock and rubbed the meaty slab up and down the long shaft. He slowly rotated his hips, grinding his ass and alternately flexing his 40 inch quads, quads almost as big as my chest. Even the muscles on the front of his shins were huge and defined. The urge to cum became overpowering. I looked down at my still soft dick and I saw how paper thin my skin had become. I must have converted 20 pounds of fat into energy and sweat.

"OH FUCK!" The scream was torn from my throat and the reverberations of that sound added to the sensations rocking my body. Logan had turned one of the shower heads on me, blasting me with freezing cold water. I felt like a newly forged sword being quenched and made diamond hard. I roared again and flexed my arms. Steam billowed from my hot skin. Orgasmic pulses surged from my balls with pressure waves travelling the length and breadth of my body. My shout was echoed by Logan as he came in sympathy at the sight of me beginning the journey I was joining him on.

I went to Logan under the showers and put my head right under the spray. I grabbed Logan's hand and even that much contact was too much for my overloaded nervous system. We stood under the cooling water, chests heaving.

"Fuck that was intense," I managed to get out on a huge exhale. •