Kenshiro (Fist of the North Star) using Tenryū Kokyū Hō to pump up his muscles, allowing him to use his full strength.
Using the cybernetic implants in his arms, Vilgax (Ben 10) pumps up his arm muscles to the point where he can destroy a mountain with a single punch.
Gyanza Rujike (Black Cat) bulks up his muscles to the point of becoming bulletproof.
In his Light of Justice form, Fusion Zamasu (Dragon Ball Super) gained a massively bulked up right arm...
...and he later bulks up even further in his rage at Vegito.
The Second and Third Grade Super Saiyan forms (Dragon Ball Z) bulk up the user's muscles immensely, the latter to the point where speed is reduced.
Caulifla (Dragon Ball Super), the first female Saiyan to demonstrate the Third Grade Super Saiyan form.
In her Super Saiyan Berserk form, Kale's (Dragon Ball Super) muscle mass increases dramatically.
Raiden's (Metal Gear) cybernetic body can expand its artificial muscle.
Vergo (One Piece) imbuing the muscles of his upper body with Busoshoku Haki.
Pica (One Piece) using Busoshoku Haki to bulk up his entire body.
Lao G (One Piece) using Jio-Ken to store up his chi from his youth, until he needs it later to boost his body strength.
Roronoa Zoro (One Piece) uses Ichi Gorilla and Ni Gorilla to pump up his arm muscles.
Monkey D. Luffy (One Piece) uses Gear Fourth by infusing his body in Busoshoku Haki and then expanding his muscles.
Gyanza Rujike (Black Cat) increasing his muscles to the max by channeling all his ki to them.
Conkeldurr (Pokémon) using Bulk Up to up its muscles, increasing offense and defense.
Everytime Gentle (Marvel) uses his power, he gets bigger and stronger.
Bane's (DC) size and strength greatly increase whenever he uses Venom.
Hulk (Marvel): The angrier he gets, the stronger he gets.
Little Mac (Super Smash Bros) after getting final smash to become Giga Mac.
Alex Mercer (Prototype) uses the Musclemass power to combat a Blackwatch super-soldier.
Ichiya (Fairy Tail) After taking a sniff of his 'Power Perfume'.
Suigetsu Hozuki (Naruto) Through the great water arm technique, can shift his own watery body fluids around to supplement his muscle mass.
At his 100% power, Frieza's (Dragon Ball) muscles greatly expand.
Cell (Dragon Ball) bulks up his muscles.
Using Gigantification, Garlic Jr. (Dragon Ball Z) gets a massive increase in muscle mass and size.
Kibano (Yu Yu Hakusho) expands his arm muscles by absorbing energy from his environment.
Toguro (Yu Yu Hakusho) can increase his muscle mass to over 100%.
Molecular muscle enhancer (Kim Possible)
Mikado Arm (Xiaolin Showdown) can enhance the muscles in the user's arms.
Metamorphia (Sonic the Comic) taking on a more muscular form.
With Migi's help, Shinichi Izumi (Parasyte) can enhance the muscles in his right arm enough to stop a speeding car...
...or bulk his arm up into a pure muscular appendage, allowing him to throw rocks with enough force to pierce flesh.
Xander Bly (Power Rangers Mystic Force) using Mystic Muscles.
Ichiya (Fairy Tail) uses Power Perfume to vastly enhance his physique to the point of bulking up his muscles and height.