SpongeBob starts his day off by posing in front of a mirror as he gets ready to make himself "large and wide." He goes to his weights, (one stuffed animal on each side) and with great effort manages to lift them over his head... and then it tips over with a squeak. Just then, Sandy comes in and SpongeBob shows off his "muscles" (stick arms), bragging about his "state of the art weight set" (more stuffed animals). However, Sandy bluntly tells him that he is not going to gain any muscle mass, (demonstrating her own in the process) unless he starts using her own personal training program. SpongeBob is ecstatic, imagining himself in various situations (flipping burgers, jellyfishing, and sleeping) with a bodybuilder's physique, and agrees to come to Sandy's Treedome at 5AM to begin his new workout.
At the Treedome, SpongeBob is put through a progressively intense series of warm-up exercises from pushups to boxing to running on a giant hamster wheel, each resulting in his arms separating from his body. Sandy now takes the less than enthusiastic sponge to the "arm cruncher", to which the sight of the contraption drives SpongeBob away, only leaving a phone in Sandy's grasp. Back home, SpongeBob is despondent (and in pain from his throbbing arms) at how difficult working out actually is... until a voice addresses him from the TV, calling him a wimp. It's a commercial for the Anchor Arms, a set of inflatable muscle balloons with options ranging from normal to veiny, and "for the ladies... hairy!", with Donald the Shark demonstrating its uses. Gary meows skeptically, but SpongeBob is interested, and goes to buy some.
Later, while wearing the Anchor Arms, SpongeBob heads towards Mussel Beach, freaking out everyone else along the way (Squidward gets his tongue stuck to his ice cream, Mr. Krabs withdraws into his shell). Once he gets there, everyone on Mussel Beach is awestruck by "MuscleBob BuffPants", and follows him to the juice bar. Sandy comes along asking where SpongeBob is, and finds him surrounded by his new fans. A short moment where SpongeBob cannot move his drink reveals the downside of his Anchor Arms: Because the "muscles" are just air inside an arm-shaped balloon, he is still a weakling, but manages to avoid detection by sipping the straw from a distance. Sandy is naturally confused as to how he managed to gain muscles so quickly, to which SpongeBob replies that he found his own secret workout." Intrigued, Sandy asks what the secret was; putting SpongeBob on the spot as everyone else also wants to know.
SpongeBob manages to fool them by claiming armpit farts are his secret workout, pushing aside skepticism by pointing out the results. Everyone else promptly begins armpit farting, while Sandy congratulates SpongeBob for finally finding a workout that works for him. To SpongeBob's surprise, she then suggests he needed to put those muscles to the test, and it just so happens the Anchor Toss Competition is today. Completely caught off guard, SpongeBob does not notice a drink being placed on top of his Anchor Arms and tries to tell Sandy he is not interested, but she decides to go sign them up anyways. Scared of being exposed, he tries to stop her, but finds himself pressured down by the drink. The panicking SpongeBob finally catches up to Sandy after the waiter takes the drink off his hand, sending him flying into the pole next to her. Unfortunately it's too late: Sandy has already signed them up, and there's no turning back.
At the Anchor Toss, everyone is preparing themselves, except for the worried and unsure SpongeBob. He nervously says he's ready when Sandy comes by to check, but quickly begins inflating more into his Anchor Arms in desperation when she turns away. Perch Perkins announces the start of the 8th Annual Anchor Toss Competition, with Don the Whale making the first toss. His anchor lands at 200 yards, with an "instant replay" crushing the hapless measurer. Next up is Larry the Lobster; the measurer, not wanting to be crushed again, tries to run out of firing range, but the anchor tracks him and crushes him at 210 yards. Sandy is up next, and launches her anchor with her signature karate kick; the measurer desperately tries to outrun the anchor, but is hit at 510 yards, putting Sandy in the lead.
It is finally SpongeBob's turn, with the crowd chanting his name as they do his armpit farting workout. SpongeBob tries to lift the anchor, but only manages to pull it on top of himself. He manages to pass it off as a joke, but knows that he cannot keep the charade up; he's going to be exposed as a phony. However, he decides he has to try anyways and blows his arms up to the JERK size, apparently breaking them. He puts all of his might into lifting the anchor, but all it does is push the air into various parts of his body and eventually the Anchor Arms explode out of overinflation, revealing SpongeBob as a weak fraud. Perch Perkins exclaims that he lost and announces that Sandy is the winner to the cheering of the fans. Sandy herself is disappointed at SpongeBob's revelation, tapping her feet expectantly; SpongeBob gets the hint and trudges after her. Back at the Treedome, SpongeBob's newest workout is to change the TV channel 100 times with his finger. Sandy figures they have finally found an exercise that works for him... just as SpongeBob's arm falls off again; He asks if she could pick them up.
The title card music "Big Ed's March" was also used in several Budweiser Super Bowl advertisements during the 2006 and 2007 NFL seasons.
There are eleven dumbbells on the title card.
SpongeBob's line of "This squirrel's trying to kill me!" would later be used by him again in "Prehibernation Week."
This is the first time SpongeBob wears a blue speedo. The second will be in "SpongeGuard on Duty."
The shark in the commercial for Anchor-Arms broke the fourth wall when he says "Hey, hey you!" in the first part of the commercial. This meant he was talking to the people who were watching the TV, but also to SpongeBob.
This is the first time a main character's name is put together with two different words. The second time was in "SquidBob TentaclePants."
"Anchor Arms" is a reference to part of an anchor called the "arm," which is the part that curves out from the bottom end of the main part and ends in the pointed part.
When SpongeBob hits the pole after Sandy finishes signing him to the anchor-toss competition, he is in his normal clothing instead of his speedo.
There are notable closed captioning errors in SpongeBob's line while he is using the telephone after the training scene.
When SpongeBob is fantasizing about having muscles, he is cooking full Krabby Patties on the grill instead of just the patty.
When Sandy is asking SpongeBob his secret, the purple fish behind her has darker eyelids than usual.
SpongeBob is weaker than normal in this episode shown not being able to pickup a glass, while he can pick up several things heavier normally in other episodes.
This is possibly due to Sandy's training, which supposedly weaken his arms.
After watching the commercial for the inflatable Anchor Arms, SpongeBob says he needs to get to the phone; although, he just got off the phone with Sandy minutes earlier, insinuating he had no phone near him, but he must've gone to the phone he just used.
The person at the bar gave SpongeBob another drink even though he didn't order one.
When SpongeBob inflates the fake arms and the inflation meter is shown, the "Hairy" setting is not on the meter.
SpongeBob is somehow able to walk with his inflated arms even though he can't pick up a glass drink and a straw with them.
During the warmup routine before the anchor toss competition, SpongeBob has to blow into both of his anchor arms to inflate them, but he only blows into one of them to inflate them both when it was his turn. This also applies when he overinflated them into the JERK size.
When Sandy is signing SpongeBob up for the anchor tossing competition she doesn't put a space between his first and last name.
SpongeBob somehow has white sleeves even though he was wearing a bathing suit.
The over-inflated Anchor Arms explodes after SpongeBob's last attempt to throw his anchor. However, the popped remains of the fake arms is shown deflating with air coming out of it instead of being completely destroyed. Also, the pressure of the explosion didn't harm SpongeBob anyways, as he still stands on the spot his fake arm exploded.
When SpongeBob is whistling, his mouth doesn't move.