The two boys headed down to an open gym along the beach. If a hot dog made their dicks bigger, they figured it was obvious the gym would make them buff.
They arrived to see guys of all ages, teenagers and young men, even a few middle aged guys. But they were all huge, as big as bodybuilers. They were also all wearing speedos. There was a bin filled with them and a sign that said speedos were mandatory. The boys ingored it.
Jack quickly went to the bench press and loaded up as much weight as he thought he could handle. Kevin spotted him. The first lift was hard, but Jack quickly gained strenght as his chest expanded. What surprised him was that all of his muscles were growing. After only a few lifts it was easy and Kevin simply watched.
Jack swelled larger and larger with every press, grunting and boning up from the thrill. His shirt exploded, revealing his giant chest and cut abs. A few more lifts and his shorts tore away. His foot long cock sprang up in all its glory.
A few of the other gym goers gave him dirty looks and one shouted at Jack. He tried to cover himself, which didn't work. The muscle teen ran back to the room. Kevin wanted to lift but followed his buffed up friend.
Back at the room Jack jerked off in the mirror while flexing his huge muscles and Kevin jerked off watching. Then Kevin began to worship Jack's huge muscles and sucked his cock. Jack shot his load into Kevin's mouth then passed out on the bed. The muscle teen still had his cock in the air.
Kevin left for the gym, but this time he went into a porta-potty and put on a speedo. He started lifting and his muscles grew bigger. Finally when his shirt and pants ripped off, the magic speedo stayed on. His boner was still big and noticeable but no one minded. So Kevin kept lifting, and lifting. He grew huge, like the biggest bodybuilder.
He headed back up to the room, but grabbed a hot dog on the way. Jack awoke to find a nude muscle hulk at the edge of the bed stroking a thick two-foot boner. It was Kevin, he was now twice as big as Jack. The muscular Jack began to worship the giant bulging muscle teen. Jack jerked his own cock as Kevin plowed his smaller friends face with his massive shaft. The muscle giant flexed his arms and they both came, with Kevin shooting a much larger load. Then the massive teen flipped his friend over and muscle fucked him.
Kevin roared and came for a full minute inside Jack.
The two muscle friends fell asleep, Jack on top of Kevin.