We already know that androids, robots, cyborgs, and other mechanical beings are stronger than organics. This is when they're constructed with the Heroic Build to prove it.
While more realistically utilitarian real-world robots often make do with a skeletal framework, real-life creators and in-universe roboticists often feel that such pragmatic designs don't do the sheer might of their robot creation justice. In such cases, the designer (which is sometimes the machine itself) goes to some effort to give themselves the outward appearance of a muscular human, often whether or not their "muscles" actually move or function as such. And while this might seem Awesome, but Impractical at first glance, one shouldn't discount the intimidation factor, as the mechanoid in question can be not only jacked, but also many times the size of any ordinary human.
Part of the growing popularity of this trope in live action comes with the increasing sophistication of CG allowing for more moving parts to be detailed and animated. It's much easier to show all those tiny components, rather than using a blocky outward appearance as a kind of SFX shorthand for "robot".
Compare Sculpted Physique. Contrast SkeleBot 9000. See also Humongous Mecha, although the style for the latter is often to render the character as if they're wearing a suit of armor, the better to emphasize their mechanical qualities. Note that while this can cover characters with Artificial Limbs, the key element is machine components built to look suitably macho. Robots and androids with artificially grown organic tissue like Blade Runner replicants or the T-800 don't qualify; see Ambiguous Robots and Meat Sack Robot instead.
- Jet in Cowboy Bebop has a prosthetic arm that looks slightly bulkier than his regular one, and the joints in particular◊ look like muscles (that or it all has muscles, but they're only exposed at the joint).
- Many cyborgs on Ghost in the Shell opt for bodies that are more than a little idealized.
- Series-wide Lancer Batou looks like a bodybuilder (and does, in fact, lift, despite all his limbs being artificial and thus gaining little actual benefit from it).
- Second-season Ghost in the Shell: Stand Alone Complex villain Kuze has a sculpted, immobile face, a well-toned body which is entirely artificial, and a lot of shirtless scenes.
- From Marvel Comics:
- Most incarnations of Ultron sport a slender build with development in the calve and bicep areas. The film version of him, pictured above, has a much bulkier build.
- Cable and the Winter Soldier as well. While not a complete robots, Cable's robotic arm is just as jacked as the rest of him. Bucky's arm is shaped to look muscular as well, but if there were a vote, Cable would win◊, hands down.
- Discussed in Meet the Robinsons, where Carl (a robot), before sending Lewis back in time, asks him to invent him with a more muscular design.
- Played with in Big Hero 6. Baymax is built with an inflatable body that gives him a roly-poly appearance. However, the armor that Hiro makes for him squeezes that figure into a more top-heavy heroic silhouette.
- Avengers: Age of Ultron: The title villain has hit the gym for his movie debut. While he is featured on the page, if you're too lazy to scroll up, just look here◊, intimidating as hell.
- Cable is shown flexing his mechanical arm at various points in Deadpool 2. While the arm is a CGI visual effect, it shows in very good detail how mechanical muscles would work.
- The Transformers Film Series: The Transformers are less blocky than their animated counterparts, particularly in the first few films, with CG allowing significant numbers of tiny moving parts to be detailed and animated, even if it wasn't always clear how they were connected.
- Champions. An early depiction of the A.I. robot Mechanon portrays him as a humanoid with artificial muscles bulging out of his arms, legs and the side of his chest.
- The RPG Cyberpunk 2020 had a limb that was a disturbing blend of flesh and metal. There was the "full conversion" cyborg the Gemini. The entire body was replaced except for the brain. The artwork was a cut-away with the metal parts made to resemble a normal human's muscles.
- From Killer Instinct:
- The series' iconic cyborg Fulgore, with the 2013 reboot focusing on his neck◊ and upper body.
- TJ Combo, with the help of Ultratech, illegally implanted cybernetics in his arms, with the form of human arms with muscles, in order to win in boxing battles Later he was discovered and kicked off. While in the first game it's not noticed because is covered with artificial skin, in KI2 it's more noticeable with his hands peeled off showing his cybernetics.
- Jack-1 through 7 from Tekken are mohawk-sporting Russian robots, with a new Jack built and sent to compete in almost ever game. Most of them have synthetic skin with obvious (sometimes glowing) seams, while Gun Jack and Protoype Jack (P. Jack) are even more visibly robotic, with squared-off metal plates and Colossus-style ridges respectively.
- Major Jackson "Jax" Briggs from Mortal Kombat volunteered to have his arms reworked with Artificial Limbs since the third game, looking very muscular. Subverted with the later games in which his arms appeared more robotic than human-shaped, but still look very muscular for a normal human anyway. One of the movies justifies it by having the robotic arms be an exoskeleton over his real (quite toned) arms.
- While not specifically human muscles, most of Horizon Zero Dawn's robots are based off animal life and have wiring that functions as muscle. The strider is the best example as most of its wiring is exposed.
- In Questionable Content, Bubbles the retired combat droid turns out to have a very defined, muscular build beneath her body armor. Justified in that android bodies use artificial muscle fiber that is presumably arranged like the organic stuff.
Faye: Is it weird to be just a lil' jealous of a robot's booty?
Bubbles: If it makes you feel any better, your tax dollars paid for it.