Rebecca had seen Zach at lunch merrily posing away - enjoying his newfound health and vitality, and when she made her entrance known he had turned red as a tomato and thanked her for the lunch. She did notice he prioritized the more protein heavy chicken she brought in, and wondered based on how pumped his new muscles were if he'd been doing some exercises in there, like push ups, sit ups or other body weight maneuvers. She had to make herself just give him the food and not make any sexual moves on Zach...
By the time school was over, Zach's curiosity had gotten the better of him. He first pulled down his tight, enormously strained underwear "just to get a look", but when Zach saw the state his cock and balls were in, he lost any fight for restraint before it had even begun.
He wrapped a hand around his newly grown eight incher and started rubbing up and down - the exact feeling was so different from what he was used to. Usually he'd shoot really fast, but it'd feel sensitive. Now, a certain amount of the sensitivity was lost, but he was lasting a good deal longer. He felt amazing doing this, watching this unbelievable hunk in the mirror jerking off. He could almost hardly believe it was this good. Almost too good to be true.
He wanted to make this last, his body beginning to be coated with a layer of sweat...
When Rebecca returned in and heard heavy grunting, light swears, and smelled the scent of sweat on the air, she already knew what Zach was up to. She stepped inside the locker room, carrying extra large clothes never claimed from the lost and found, and said, "Zach I need you decent!"
Zach immediately halted and groaned, the idea of stopping his masturbation seemed so distant, so difficult, but he sighed and forced himself to stop. He put his underwear back on, groaning as he felt how tight it was especially with his organ now engorged. "Did you have to blueball me?"
Rebecca entered and saw him standing there in his underwear, and handed him the momentary substitute clothes, "Put these on..." she was blushing now herself, feeling like Zach was just overwhelming in how attractive he was in his mid to late thirties. "...We need to get you new clothes..."
For the massive bodybuilder Zach had become, even these new clothes were tight fits, and so he was not quite comfortable as he and Rebecca headed out from the school - first to her car, and then driving down to a local sports store. Zach started pondering what kind of clothes he wanted for his new physique. Man it was still so overwhelming that he was looking so ripped! And...damn, he had NOT calmed down at all. Thank goodness the large pants he was wearing now obscured his groin.
Exiting the car wearing said large pants, a hoodie and a tank top underneath it, Zach and Rebecca entered the sports store. Zach pondered about some things as he looked around the store. This was just so...exciting. He was hanging out with the teacher he'd now grown to have a bit of a crush on...literally...and she was gonna be getting him clothes!
"New boyfriend, Becky?" The desk lady asked, blatantly checking out Zach. "Mm, mm...he is such a hunk! Where'd you find him?"
Rebecca answered, "Oh, met him at the gym. He's such a sweety."
"Yeah, I uh..." Zach started, "I met her at the gym. My name's Zach. I'm a uh...a physique bodybuilder. And I was...helping her with an exercise and we...uh...yeah."
Rebecca figured it was good to get Zach rolling with it to have less awkward questions, and led the way over to the sports gear area. Zach's eyes went over all the many shirts, stringers, tops, shorts, tight pants, gear...damn. He'd only ever seen this kind of stuff on the jocks at school. And now...now he could actually wear it himself!
Picking out a few stringer shirts and some shorts, he brought the clothes over to Rebecca with a wide grin on his face and almost bounced along with her back to the front desk. The desk lady winked at him as Rebecca walked off with Zach, blatantly checking out Zach's muscular ass.
Out in the car, Rebecca thought about what to do now...