Rockersize is the twenty-seventh episode of Grojband. It was originally released on Cartoon Network's website and mobile app in May 2014. However, it did not air until Boomerang broadcast it on February 22, 2015. This makes it the first episode to originally air on Boomerang, and also makes Grojband the second show (after Numb Chucks) in which Boomerang aired new episodes of, as well as the first show that Boomerang aired new episodes of after it was originally cancelled by another network.
Corey offers three impromptu tickets to some old ladies who take gym class.
The episode begins with Buzz Newsworthy interviewing Gym Barney at the Gym Barn. He asks him why the people there are all so weak and wimpy. Gym Barney tells him that he has no idea why none of them are being strong like they usually are. Corey and Laney are in the garage, watching the news and Corey says that the reason why their all being so wimpy is because the music that he's playing there is so depressing that it's depriving them of motivation to work out. Kin and Kon are seen trying to work out to the same music and they are sweating and exhausted. Kin says that he would be doing so much better if it weren't for the bad music. Corey gets the idea to play some of their music at the Gym Barn to motivate the people there to work out better.
At the Gym Barn, Nick Mallory is working out along with Trina and Mina watching him. Trina yells at Mina and tells her to stop bending better than her. Nick Mallory tells Trina that he's completing a new workout plan that's going to get him a seventh ab and Trina asks him if she can watch so that she can learn how to do it. Grojband walks into the Gym Barn and they tell Gym Barney that if he wants his workers to toughen up and do better at working out, he has to play some more motivational music. Barney tells him that he wishes that he could, but he doesn't have any other songs on his non-brand name personal music player. Corey tells him that if he can't use any of his music, then he suggests that his band plays music for them. When Trina hears this, she get mad and tells him that there's no way that he's going to play there. Then, Barney takes Corey and his band to another room where he has three old ladies that work out there. Their names are Blanche, Bertha and Beatrice. He tells them that if he can motivate them to work out, then he will be able to play music at the Gym Barn any time they want. Trina walks out of the room in anger telling them that they have no chances of being able to rock them into shape.
Blanche, Bertha, and Beatrice nag Grojband about trying to rock them into shape. Corey says that instead of spending fifty weeks in there, playing music for them, they're going to compress fifty weeks worth of music into five seconds. Laney sarcastically asks him if they're going to do that by having a thousand hands. Kin and Kon look into the vending machine and are mesmerized to see Jack Attack Energy Bars in there. Kin says that Jack Attack Energy Bars are energy bars that are so powerful, that they got taken off the market because one guy ate one and it turned him into pure light. Apparently there are four of them left over and they were in the vending machine. Grojband gets the energy bars and they all eat them. This gives them a blast of energy which makes them play rock music so fast, they they compress fifty weeks worth of it into five seconds and they blow up the stage and shatter all the windows of the Gym Barn. The side affects cause Blache, Bertha, and Beatrice to become really big and have overgrown muscles. They all break out of the Gym Barn and run around Peaceville forcing everybody to be proper. Kon turns on the TV and it shows a news report with Buzz Newsworthy and Chance Happening who are reporting the three old ladies running around the town and forcing everybody to be proper. They go to a live interview with them where they apparently forced Mayor Mellow to agree with them and make Peaceville be quiet. The band goes outside and everything seems pretty normal at first, until Bertha jumps up and flicks a man across the town and makes him land in an explosion because he didn't help her cross the street. All around town, Blanche, Bertha, and Beatrice are causing this kind of trouble. Sparkles is barking at everybody and scaring them. This makes Blanche come up to his owner and nag him for not putting him on a leash. She put a leash on his owner and punches him around and then sends him flying. Captain Tighty Whitey, Shaven Beard, and Barnacle Tim are dancing to sea shanties until Bertha gets on their ship and yells at them for playing their music too loud and then smashes it, making it sink. At the Indie 400, Blanche is forcing the racers to move along the track very slowly so that they don't make too much noise. One of them jets off really fast and then Beatrice smashes it with her fist, causing the racer inside of it to get crushed into a cube. She yells at him, telling him to be safe when driving. At this point, Grojband realizes that the old ladies have taken things too far.
Back at the garage, Corey says that the grannies have taken over Peaceville. Kon suggests that they call them "Grannapes" but then Kin argues with him, saying that they should call them "Gorillandmas" instead. Corey says that in the garage, they can still be Grojband and then he takes out his guitar and shreds on it, causing an electric sonic wave of music to burst out from it. Blanche bursts into the room and threatens to "cut me a switch" if they don't be quiet, she leaves the garage telling them that bedtime is in five minutes. This finally makes things bad enough for Corey to want to do something about the situation. Kon turns on the TV to the news where Chance is telling everybody to go to bed before the old ladies find them. Beatrice comes up to her and cleans all the make up off her face. This gives Corey an idea on how to make Trina go into Diary Mode. Laney tells him that lyrics aren't going to help. Corey tells him that if they play slow metal, that it might turn them back to normal again. He also picks the name "Gorrilandmas" over "Grannapes."
The plan is put into action. Kin starts roller skating down the street while playing a trumpet really loudly. He is also eating pretzels as his prize for coming up with the winning name. He lures the Gorillandmas to the Gym Barn by eating after breakfast and making lots of noise. Inside the Gym Barn, Nick is doing sit ups and Trina is watching him. Nick is trying to grow a seventh ab. Corey tells Trina to count Nick's abs. Trina demands him to get out of the Gym Barn. Kin rushes by and the Gorillandmas bust in. Corey tells the Gorillandmas that there's a girl touching a boy and he points to Trina and Nick. Bertha picks her up and extends her skirt because it seems too short. Blanche throws her into a bag, and shakes her around. When she comes out, she is wearing old fashioned clothes. Beatrice wipes all of her make up off. Bertha pulls her hair back into a bun, stretching her face back and then tells her that there's going to be no kissing until it's proper. Bertha tells that that it will be proper in ten years. Trina runs away screaming in fear but then Beatrice grabs her. Trina gets so mad about the Gorillandmas and how they're making her live, that she goes into diary mode. Corey gets her diary and and his band sing the song Yesterday.
After the song, Nick grows a seventh ab and Trina goes insane with love. Meanwhile, Mina is still stuck in her stretch. The Gorillandmas went to sleep because of the song and Corey had finally put an end to the problem. Laney says that the Gorillandmas will probably be back to normal again after forty nine more classes. He tells his moral for the day and then Kon asks him if they helped Barney by doing what they did. Corey doubts that he helped them and then he closed the garage door and ended the episode.