Ed wanted to be better and was focused on getting to Erik, not focusing so much on the transfer he was initiating. In the bottom of Ed's mind he was taking a trait from Erik. Having not explicitly focused on copying it, he stole it.
Ed watched in shock as Erik withered before him. The man who exuded masculinity throughout his highschool career, having led the school championships and bringing home awards, regressed in seconds. The glazed look in his eyes remained as his ample body hair regressed and his muscles shrank. It was obvious that his testosterone level dropped significantly, which made sense from your earlier research surrounding your own side effects, maintaining muscle mass increases testosterone, working out increases testosterone. Erik, in this new reality, did neither.
To your surprise, you watched his now spindly frame thicken again, but not with muscle. Erik filled back out and where his hard and defined pecks were, saggy moobs took their place. His belly which was flat expanded to a paunch and continued to grow until he was beyond stocky and definitely fell into the category of being fat. The expansion was not limited to his stomach, still having the zombie like expression, he repositioned his feet as his thighs undoubtedly underwent the same growth his stomach, chest, arms and now double chin did. The stubbly shadow on his face thinned, but then a beard exploded out, being one of the few things left that helped him express his masculinity. Apparently, as his development lagged behind his peers, his desire to work out or do anything physical, ceased.
Ed was entirely fascinated by this unexpected turn of events, and was lost in thought piecing together this unexpected turn of events as Erik got dressed in clothes he now filled out in a completely different way.
Erik noticed Ed staring at him with a completely perplexed look on his face, "Is something wrong?" Erik asked cautiously.
Ed was suddenly pulled out of his head realizing he was being impolite and put on the spot, "You..." Ed didn't know what to say.
Erik turned bright red and scowled, immediately taking offence and knowing this genetically blessed kid was just looking for a way to insult him. Its bad enough that he has to deal with comments and stares daily, but just last week he had his physical exam and his doctor reiterated that he needs to do something about his weight. So here he was, trying to exercise alone, and he still gets mocked.
Hot tears of fury welled up in Erik's eyes, "I'm just leaving, Leave me alone!" he growled at Ed and immediately blew past, and out the door.
Ed was dumbstruck, he didn't want to steal Erik's strength but even more so, couldn't understand what just happened. With the locker room to himself, he put that aside and went back to admiring himself in the mirror. He was significantly more masculine than his older brother now. By appearances, he and his brother could both pass for being the same age, but due to him being more muscular, Ed recalls people (annoyingly) calling him Jacob.
The bell rang, He has two minutes to get to class and his ripped shirt and now much too small jeans make this seem like it was a poorly thought out plan.
Ed also didn't consider, and isn't thinking about the fact that he still has most of his puberty to go through. Erik, who was mostly done with puberty, has little to no hope of regaining what he doesn't know he had. Although he could, even getting to a healthy state seems impossible to him. As it stands, Erik will probably spend the next decade, or possibly the rest of his shortened life, riding the edge of morbid obesity, but who knows? It can all change in an instant.