"Growing Muscles" Sequence

A sub-trope of Transformation Sequence where increase of muscle mass and definition is prominent. It can be used by a character transforming to his superpowered form, as well as a visual indicator of a Super Mode activating. In either case, those subjected to it are generally expected to possess Super Strength.

The sequence usually consists of close-up shots of various muscle groups, most commonly the biceps, chest and back, growing and becoming more defined. As a result, expect Clothing Damage (with the exception of Magic Pants). The transformation doesn't have to be limited to changes in musculature; for example, a villain can have Spikes of Villainy popping up along the spine of his expanding back. Bulking up is also unexpectedly common in modern werewolf transformations, despite the wolf being an animal generally regarded as lean rather than massive.

Depending on the character and the setting, a Growing Muscles Sequence can be Voluntary Transformation or Involuntary Transformation, range from painless to Painful Transformation to a Body Horror and its end result can run the gamut from having a Heroic Build to being The Grotesque.

Compare Shapeshifting, One-Winged Angel, and Hulking Out. See also Shapeshifter Baggage, Temporary Bulk Change.

Examples of "Growing Muscles" Sequence include:

Anime and Manga

Used all the time with various kinds of Super Modes in Dragon Ball.
Done in Hunter X Hunter when apparently 12-year old Biscuit Krueger goes from looking a cute schoolgirl to being 10' tall and incredibly ripped.
Kid Muscle from Kinnikuman Nisei.
Kotetsu from Tiger and Bunny, though it turns out it's a cosmetic feature of his original super suit.
Younger Toguro from Yu Yu Hakusho goes through this every time he unleashes a percentage of his full power, assuming ever more ridiculously bulked up forms during the course of the series. A less prominent example from the same series is Byakko, who grows as he absorbs the blows of his opponents, which turns out to be his undoing.
In Bleach, Ggio Vega and Poww do this when they decide to unleash their full power. Later on, fullbring forces a yakuza trapped inside a weaponised plushie to go through one of these.
Aisha Clan-Clan in Outlaw Star can transform into a more muscular version of herself under a full moon. (And then further into a non-anthropomorphic panther creature.)

Comic Books

The Hulk in all his incarnations. He is, after all, the Trope Namer of the related trope Hulking Out.
- Likewise, but to a lesser extent, his cousin Jennifer. Whether or not she goes from mousy and unassuming to tall and athletic to flat-out ripped depends on who's drawing her (the same applies to the other She-Hulks, Lyra and Red She-Hulk). On special note is her transformation in the 90s cartoon, mainly due to the level of muscularity she's shown with (she was slimmed down considerably in the second season) and... well... the fact that it's "lighting her fire".
In The New Universe, David Landers of DP 7 goes through quite painful transformations when he grows muscles, which he has to sustain by being a Big Eater.
Patriot of Young Avengers, in the storyline where it's revealed he takes Mutant Growth Hormone. He injects himself with too much, and grows to the size of a truck.
Some Marshal Law superheroes "pump ions" to bulk up.
This happens to Caitlin Fairchild in the first issue of Gen 13. She goes from short and slender and mousy to tall, ripped and stacked once her powers activate.
In his first appearance, Nightwing villain Blockbuster has one of these, turning him into a giant, deformed monster. Unlike most examples, the effect is permanent.

Film

Bane's initial transformation in Batman and Robin.
Tim turning into The Muscle in the Imagine Spots of The Dangerous Lives of Altar Boys.
Dr. Jeckyl in The League of Extraordinary Gentlemen does this when he changes into Hyde while underwater inside the Nautilus.
Happens to Scrappy Doo in the first |Scooby Doo movie, and to Shaggy in the second, although the causes and intentions for each are different.
The Nerdlucks turning into the Monstars in Space Jam. Bugs Bunny, being a Looney Toon, is not above faking one to convince his teammates that "Michael's Secret Stuff" works.
Violator in the Spawn film.
Done quite naturally in the film The Three Stooges Meet Hercules, as the nerdy but affable Mad Scientist labors in a rowing crew aboard a galleon. The strain of pumping the oars causes him to bulk up significantly, with many shots of his bulging biceps, until he is a match for the mythological strongman himself.
During the climatic fight of Dabangg, the protagonist makes to look like he grew such muscle he rips off his shirt.

Live-Action TV

Mahou Sentai Magiranger and by extension Power Rangers Mystic Force: one of the Green Ranger's spells.

Video Games

Altered Beast has your character undergo two such transformations for the first two Power Ups he collects in a stage. His transformation into a beast once they pick up the third also has elements of this.
Batman: Arkham Asylum has this happen to a depowered Bane and some of Joker's goons when they get injected with "Titan", a derivative of the Venom normally used by Bane. It almost happens to Batman when he takes the bullet for Commissioner Gordon, but he's able to resist the transformation until he takes an antidote. The Joker, on the other hand...
Rick undergoes a pretty gruesome one in the opening cutscene of the updated Splatterhouse.

Terror Mask: Aw, quit whining. Did I say it was gonna be fun?

Webcomics

Ace Dick's transformation into Fiesta Ace Dick in Problem Sleuth.
Doc Scratch's corpse's transformation into Lord English in Homestuck

Western Animation

Done in a number of werewolf transformations in animation. Apparently the "were" in "werewolf" is the Anglo-Saxon for "bodybuilder".
Bane in Batman the Animated Series and The Batman.
Ben 10: Vilgax in the early seasons had Cybernetic Spikes of Villainy that did this.
Raimundo from Xiaolin Showdown had this issue when the Shen Gong Wu kept magnetically pulling towards him, making him increasingly more powerful to the point he was virtually invincible, with Wuya attempting to use him as a vessel for her to defeat the monks.
One of the effects of the Super Soldier Serum that created Captain America (comics).
Prince Adam's transformation to He-Man and the Masters of the Universe usually doesn't involve this, despite the former being an ordinary Eternian and the latter "the most powerful man in the universe". In the first series, this was because He-Man is pretty much Prince Adam with a tan and less clothes on. In the 2002 series a sequence is used for a few episodes in the second season, until He-Man gets his armour.
Justice League Unlimited in the episode "The Patriot Act" after a mad general steals super soldier serum and injects himself.
A couple of Timmy's wishes in The Fairly OddParents resulted in this.
Billy turning back into Ganthar in Martin Mystery.
In each episode of The Miniavengers, a kid will pass through a momentary but incredibly exaggerated sequence before getting their superpower, temporarily ending up dozens of times the size of the earth.
Popeye, every time he eats his spinach. The change is brief and usually located in the (already abnormally muscular) forearms, sometimes with a superimposed image of a battleship, a cannon, a high-powered turbine or similar imagery.
Munya from The Secret Saturdays.
The Simpsons: Bart has an Imagine Spot where he's a professional human guinea pig. He takes one sip of Nature's Goodness soda and turns into a deformed monster.
Super Duper Sumos is a rare case where the characters are already bulky; what they are gaining in the transformation is definition.
The Totally Spies! episode "The Incredible Bulk" featured a plot involving power bars that would cause anyone who ate them to go through a series of such transformations, until they would finally explode.
Prime and Hardcase from Ultraforce. For the former it's a standard transformation sequence, for the latter a permanent change.
Happens to Jade from Jackie Chan Adventures in the episode "The Amazing T-Troop" when she uses the ox talisman. Interestingly, while the ox talisman does grant the user the power of super strength, this is the only occurrence where this trope is applied.
A sequence depicting this happening is often played when Kaeloo transforms into Bad Kaeloo. The most attention is paid to her buttocks.