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 tips over with a squeak. Just then, the doorbell rings; it's Sandy! 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's 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 muscles 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 intrigued, and goes for his phone.
Later, with his new Anchor Arms attached, 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 downside of his Anchor Arms: Because the "muscles" is just air inside a muscle 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 doesn't notice a drink being placed on top of his Anchor Arms and tries to tell Sandy he isn't interested, but she decides to go sign them up anyways. Scared of being exposed, he tries to stop her, but finds himself anchored down by the drink. The panicking Spongebob only 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 terrified Spongebob. He nervously says he's ready when Sandy comes by to check, but quickly begins puffing air 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 a karate kick; the measurer desperately tries to outrun the anchor, but is crushed at 510 yards, putting Sandy in the lead.
It's 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 can't 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. He puts all of his might into lifting the anchor, but all it does is push the air into various parts of his body before the Anchor Arms explode, revealing Spongebob as a fraud. Perch Perkins announces that Sandy is the winner to the cheering of the fans. Sandy herself is disappointed at Spongebob's deception, tapping her feet expectantly; Spongebob gets the hint and trudges after her. Back at the Treedome, Spongebob's newest workout is to change the channel 100 times with his finger. Sandy figures they've finally found an exercise that works for him...just as Spongebob's arm falls off again; He asks if she could pick that up.
Shower In A Can!
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The billboard sign with beachgoers working out reads "Mussel Beach," instead of "Muscle Beach." This is a reference to the tiny shell-covered creatures commonly found on beaches.
The title card music "Big Ed's March" was also used in several Budweiser Super Bowl ads during the 2006 and 2007 NFL seasons.
Sandy technically didn't throw her anchor like the others, she just threw it in the air and kicked it when it came back down.
SpongeBob's line of "This squirrel's trying to kill me!" would later be used by him in "Prehibernation Week."
The shark in the commercial for Anchor-Arms broke the 4th 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."
Tiny Tim is referenced in this episode. "Who were you expecting, Tiny Tim?"
Scooter mentions the episode title when he says, "You mean 'MuscleBob Buffpants' ? He's in there."
"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 bathing suit.
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.
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.
The man who measured the anchor throwing distances was far from the other anchors after Larry the Lobster had his turn, but when Sandy had a turn, the man was next to the anchor before running around in circles.
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.
When Sandy is signing SpongeBob up for the anchor tossing competition she doesn't put a space between his first and last name.