Heavyworlder

A common trope in Science Fiction, the Heavyworlder is someone who is adapted to life in a high-gravity environment - either a human being who has been altered to survive through Genetic Engineering or Hollywood Evolution, or an alien who evolved on such a world in the first place. One factor common to nearly all Heavyworlders is prodigious physical strength (even though logically, physical stamina would be more important when carrying around twice your weight every day). Another common element (one could even call it a fallacy) is that many Heavyworlders are described as being far larger and more massive that normal humans, despite this adding even more weight for them to carry around—in fact, basic mechanical considerations and Square-Cube Law shows that it's much more advantageous for heavyworlder to have a compact, stout, but short body, not unlike common portrayal of Dwarves in fantasy. Usually they have personalities to match (imagine an entire race as The Big Guy). A few exceptions are noted below. In fights, a Heavyworlder is usually a One-Man Army.

"Lightworlders" -- skinny, delicate humans from low-gravity habitats, or orbital colonies without artificial gravity—aren't nearly as common as straight treatments, as it's harder to portray your Big Damn Heroes as Badass if they're built like toothpicks. Low-gravity characters are often female, fragility being more forgivable in women to most writers. Truth in Television here - astronauts on extended missions have been known to undergo growth spurts, long bones lengthening and the resultant bone is very, very brittle.

Ordinary humans who visit low-gravity planets, and seem much stronger there than on Earth, are a Humanity Is Superior variant. While this variant is common in vintage scifi, the natives of such worlds are seldom portrayed as skinny, fragile inversions of this trope. That's probably because it makes for poor Fan Service if the Damsel in Distress rescued by the "incredibly strong" human hero makes Olive Oyl look like Pamela Anderson.

In reality, it is unlikely that any of these tropes would work; species generally survive best in the environment they're adapted to, and, as noted above, real-life astronauts who spend significant time in low-gravity situations rapidly suffer health problems, especially muscular and bone degeneration.

Anime and Manga
"Vegeta: "Maybe... if your planet had five hundred times Earth's gravity, you'd have an advantage, but ten? I don't even feel it!""
 * Similar to Superman, Dragonball Z has the Saiyans from Planet Vegeta, with gravity 10x that of Earth. The saiyans also routinely train in high-gravity chambers, beyond 150 times Earth's gravity in some cases. This was used hilariously when a lower level Elite Mook in the beginning of the Buu saga challenged the Saiyans, thinking that changing the environment to his home planet, which had 10 times Earth's gravity, would give him a sizable advantage. Boy was he wrong.


 * The series also gets around the whole issue of heavyworlders logically being short by having the Saiyans be invaders from another planet, which presumably had gravity to closer to ours. Indeed, Vegeta's original inhabitants, were noticably smaller than humans.
 * Vegeta himself is a bit short...but that's just him specifically. The other Saiyans we see (including his father, the late King Vegeta) would range from average height to very tall by human standards.
 * One of Rumiko Takahashi's comedic one-shots was Maris the Chojo, about a bounty hunter whose family was from a high-gravity world, and had proportionate strength, so they had to wear special restraints in order to keep from destroying everything around them by accident. The antagonist was also a super-strong heavyworlder, though not to the degree of the protagonist.
 * Not a person but a machine: in Zeta Gundam, Big Bad Paptimus Scirocco's final mobile suit, The O, is designed for operations in Jupiter's gravity. As such it's incredibly heavily armoured and features massive thrusters to allow it to move at all. Turn it loose in space or Earth's atmosphere and it becomes a Lightning Bruiser and One-Man Army.

Comic Books

 * Charlie-27 of Marvel Comics' Guardians of the Galaxy is a Jovian, huge, super-strong, muscular and very tough. The genetically engineered Jovians lived on floating gas-mining cities in Jupiter's atmosphere, prior to their genocide by hostile aliens.
 * Tom Strong was raised in a high-gravity environment, giving him immense musculature and strength while somehow not interfering with his growth. Just the opposite, in fact, he's huge (the goloka root might have something to do with that).
 * Buck Godot, Zap Gun For Hire is a Hoffmannite, from a violent race of large heavyworlders who call normal humans "jellybones" and are prone to Attack Hello. Hoffmanites tend towards the "big and portly" -type, but they were also genetically engineered by a team that thought that making a sub-race of centaurs was a good idea.
 * Before he started flying and shooting laser beams out of his eyes, the late Golden Age and full Silver Age explanation for Superman's powers was that his home planet, Krypton, had exceptionally high gravity (the first explanation given in Action Comics #1 was Evolutionary Levels—Superman had originally been conceived as being from the future). Even after the yellow sun explanation came into play, Krypton was still described as having a much greater mass than Earth. This might be the inspiration for Tom Strong's origin.
 * Elliot Maggin, a prominent Superman writer, once wrote that Krypton's gravity was so great that every explorer from another planet who had landed on, or even approached Krypton was unable to to ever return. Krypton gained an ominous reputation as a "black hole planet", whose gravity was inescapably strong.
 * It apparently wasn't inescapable to Kryptonian rockets, which were rarely used before Jor-El shot Kal off because Krypton was such a paradise, there was no reason for the Kryptonians to try and leave via a space program.
 * Possibly as a reference to this fact, Stan Lee's presentation of Superman was a policeman from an alien world with high gravity.
 * Not quite the same thing, but the idea that Aquaman's incredible strength and durability come from he and his fellow Atlanteans adapting to the "crushing ocean depths" is related to this trope.
 * Thondar Allen, a "fifth-generation Jupiter colonist" and distant future descendent of Barry Allen, who appears to exist largely for the visual humour of a really massive speedster.
 * Frequent foes of the Legion of Super-Heroes are the humanoid Khunds (no, I'm not going to ask how you pronounce that.)
 * The Kree are a Marvel Universe race stronger than humans and just as bastardly—think Nazis with Star Trek technology. Only a small pacifist cult keeps them from falling into Exclusively Evil.
 * The supervillain The Persuader from The Legion Of Super-Heroes is a normal human, but has incredible strength from being born and raised on a high-gravity world.

Film

 * The Phantasm films have dead humans resurrected as superstrong dwarves by compacting their density on a high-gravity world in an alternate universe.
 * The creature in the B-Movie It Conquered the World (1956) was originally conceived as short and squat, due to the heavy gravity of its native planet. Actress Beverly Garland was unimpressed by the vertically-challenged villain—approaching it within hearing of director Roger Corman she cried "So, you plan to take over the world do you? Take that!" and kicked it in the head. Corman agreed to redesign the creature to more menacing proportions.
 * Officially, Jek "Piggy" Porkins from A New Hope - the first pilot to die on the run against the Death Star - was from a high-gravity world. He was somewhat overweight but still strong.
 * Several minor characters and extras in the Star Wars Expanded Universe are also mentioned to be heavyworlders—however, unlike Jek, they're generally portrayed as being short and stout. In fact, it could be that Jek Porkins was adapted to a heavy world, and gained weight from the sudden drop in exercise upon moving to standard-gee worlds.
 * ET should have a category all to himself in between these two, having the lower body of a heavyworlder and the upper body of a lightworlder.

Literature
"Q: How many Jinxans does it take to paint a building? A: Three. One to hold the paint sprayer and the other two to shake the building up and down."
 * The Jinxians of Larry Niven's Known Space are one of the rare short heavyworlder variety (described by one character as "five feet tall and five feet wide"), realistically so, since human growth patterns are determined in part by the weight of the body. They are strong enough to bend crowbars, and black-skinned regardless of ancestry, since the star they orbit, Sirius, is far brighter than Sol, particularly in the ultraviolet. They got this way after only four hundred years of selective breeding, but the downside is heart problems and short lifespans even with the life-extending drug "boosterspice". Culturally, they are mainly scientists and punsters.
 * Ringworld even features a joke about them:


 * Anne McCaffrey's "Planet Pirates" series (Dinosaur Planet, etc.) may actually be the Trope Namer. The genetically-enhanced Heavyworlders, due to their history, resent and distrust "lightweights" to the point of being open to manipulative propoganda and conspiracy theories by the titular criminals. In a greater society of near-universal vegetarians, they also have to eat meat due to their altered metabolism.
 * The Lensman series featured a company of Valerians, the next-millennium descendants of Dutch colonists on a high-gravity world, serving in the Space Marines of the Galactic Patrol. In close quarters, their Weapon of Choice was the space-axe, essentially a solid-metal combination axe and warhammer pragmatically adapted for zero-G and inertialess combat.
 * Another of E. E. "Doc" Smith's great sci fi series starred the Family d'Alembert, a circus troupe of heavyworlder secret agents and incredible badasses, one and all.
 * The CoDominium universe has the inhabitants of Frystaat, a Death World with high gravity, intense heat, blinding sunlight, and native life with More Teeth Than the Osmond Family. A mere six hundred years of mutation and natural selection has rapidly transformed them into superhumans with strength, stamina, senses, and reflexes beyond the human norm (almost a match for the Saurons). They are, however, very vulnerable to cold.
 * Honor Harrington herself is from a world with heavier-than-normal gravity, and the genetic enhancements built into her for survival on that world are part of what make her kick so much ass. The series also has San Martin, the highest gravity planet inhabited by humans with several minor characters being from there. Inhabitants are noted for their prodigious strength and muscle mass.
 * One story by Stephen Baxter had "humans" engineered to live on neutron stars. Said "humans" were on a microscopic scale - such that they considered a centimetre to be a really impressive size for a city - and lived inside the star. Oh, and got around by "swimming" through the magnetic field...
 * Bill the Galactic Hero by Harry Harrison. The Chingers are lizardoids only seven inches high, but as they come from a 10G world, they're able to throw the Space Trooper protagonist easily. Government propaganda portrays them as being seven feet tall so morale won't be affected.
 * A short story by Gordon R. Dickson adds a forgotten corollary: things fall faster (or rather, accelerate at a higher rate) on a high-gravity world. One alien from such a world is somewhat stronger, but much faster, because falling over on such a planet is a bad idea and being able to catch falling things is usually helpful too.
 * The S't'ach in Star Trek: Titan, who resemble metre-high four-armed blue teddy bears, but are denser than they appear. In early books they are said to be superdense, but in a later book one points out the perils of having a lot of mass on a high gravity world. Apparently, this is a rumour spread by the S't'ach themselves; they're aware of how cute they look to humanoids, and want to discourage them from trying to pick them up and cuddle them.
 * The Perry Rhodan universe features human colonists that come in short-and-squat, physical giant, and even relatively normal looking superman form depending on their exact planet of origin.
 * The Brobdingnagian, from the Hoka story "The Napoleon Crime." Who's also a Gentle Giant and a Japanophile, and would be obnoxiously cute if he weren't huge. With delightful appropriateness, the illustrations for "The Napoleon Crime" were done by Phil Foglio, creator of heavyworlder Buck Godot.
 * Harry Harrison's Deathworld features Pyrrus: double Earth gravity and so, so much more. The population are all TykeBombs. Pyrrans are short and massive, for added realism.
 * Used in George R. R. Martin's "Thousand World" stories. In the short story "The Hero", the planets Wellington and Rommel have habitable climates but higher-than-Earth gravity, and their populations were recruited by the Federal Empire of Earth as soldiers.
 * The "1 on 1" gamebook Battle For The Ancient Robot had Kan-Tal from Jupiter as one of the human player's allies. His vital stats are given as 5' 2" and 492 pounds.
 * The people of Lusus, a very massive planet with its settlements buried underground (called Hives and many of them fitting the description), are described as being rather short, rather stout, and very strong in Dan Simmons' Hyperion Cantos. This includes Brawne Lamia, a Private Detective from Lusus who fell in love with a clone/reconstruction of John Keats who had lost his memory...and long story short, that's how she ends up one of the main characters of the first novel.
 * The people of Sol Draconi Septem, which in addition to being very heavy was covered in a mostly-frozen atmosphere (or something), are described in the third novel (Endymion) as being rather like short, stout Inuit.
 * The inhabitants of the planet Mesklin (which not only has high gravity, but a rather odd rotation) in A Mission of Gravity by Hal Clement are adjusted to this by looking somewhat like flat centipedes. The Mesklinites are the main characters of the story, which tells how a brave sea merchant retrieves a probe fallen from the sky for a strange space alien (i.e., a human).
 * In Last and First Men, Olaf Stapledon describes a realistic version of heavyworlders engineered to colonize Neptune (at the time it still seemed possible): they're simply midgets who take advantage of the Square-Cube Law. Subsequent Neptunian species engineer themselves to be taller than the original terrestrial men, but it's made clear that they're so advanced they're not limited by petty biological constraints.
 * Saval Bork from Steve Perry's Matador Series is from a heavy-g world, and has some genetic modifications to help him survive there. He also spends a lot of time weightlifting, when he's in places with lighter gravity. His personal record in the bench press is 360 kg, or approximately 790 pounds.
 * Averted (as per usual) in the Sector General series, with the FROB Hudlar (homeworld in excess of 3G, body plan more or less spherical with six prehensile tentacles) and FGLI Tralthan (homeworld 2G, rather like a hexapedal elephant, can easily be killed by a fall).
 * The Starwolves in Edmond Hamilton's Starwolf trilogy are Vikings In Space from the heavyworld Varna. They can endure higher-acceleration maneuvers than anyone else they've encountered, which is what makes them so dangerous and hard-if-not-impossible to catch. "When a Starwolf gets killed, they declare a holiday on all decent worlds."
 * Implied to be true of the Jenoine, from the Dragaera series, as they have sturdy, heavily-muscled bodies and the world on which they imprison their captives in Issola has higher gravity than Vlad and his friends are used to. Only an implication, because it's unclear whether the prison-world in question is the Jenoine's native habitat, or if its higher gravity is just a coincidence.
 * The Masters in The Tripods had evolved in a higher gravity world and built domed cities to maintain a higher pressure to accomodate both this and their need to breathe an atmosphere other than Earth's. It didn't have a good effect on their human servants.
 * Reconstructed and downplayed in The Right Hand of Dextra: While Dextra's gravity isn't that much higher, the protagonist speculates that the colonists' descendants will be heavyworlders, albeit a more realistic take on the idea (short, stocky, and thick-limbed).
 * Dragons Egg features one of the most extreme examples and yet manages to treat it realistically—like the Stephen Baxter example above, the Cheela live on a neutron star with a gravity 67 billion times stronger than Earth's. They're essentially puddle-like Blob Monsters, since nothing could stand on legs on their homeworld, and made of degenerate matter for even ordinary atoms fold themselves in that gravity.

Live Action TV

 * In Star Trek, Vulcan is said to have higher gravity than Earth, and Vulcans are consequently around three times stronger than humans. This explains why Spock, in spite of being a nerd, can kick most people's butts in hand-to-hand combat.
 * There's also the fact that while Vulcans turned away from their previous proud warrior race society thousands of years ago, they kept teaching the old (and very effective) martial arts as a matter of tradition.
 * In Andromeda, there are several genetically-engineered human variants, including people who breathe water and Heavyworlders. Captain Dylan Hunt's mother is a Heavyworlder, so he has genes that almost make him a physical match for a Nietzschean Super Soldier.
 * In a straight fight against a Nietzschean with equivalent hand-to-hand combat, he'd lose. This is acknowledged by the producers in commentary tracks. though that's a Retcon added by post-shark writers.
 * An episode of the Buck Rogers TV series had an unassuming man of average build named Toman who was secretly from a high-gravity planet, giving him great strength, which he used as a hit man who never needed weapons.
 * The Sontarans, a race of cloned galactic warriors from Doctor Who. Although Sontarans 'grew' in size over the course of the series, the new series took the trouble to restore them to their original short height, leading to the inevitable Hurricane of Puns from the Doctor.

Tabletop Games

 * The Squats of Warhammer 40,000 evolved on high gravity worlds back in the days they weren't wiped out by the Tyranids. (And then subsequently declared to have never existed.) As did the Ogryns, who survived without being lunch. The planet Catachan, on top of being one of the nastiest jungles in fiction, also has a slightly higher gravity, giving Catachan natives the somewhat unflattering nickname of "Baby Ogryns".

Video Games

 * Taken to an extreme by the 'lobster' form that Kheldians can take in City of Heroes; a previous common host for Kheldians were the inhabitants of a white dwarf star.
 * According to official data, The Covenant has a few heavyworlders in its ranks. The Sangheili/Elite homeworld Sanghelios has 1.375G, Doisac (the Jiralhanae/Brute) homeworld has 2.1G, and the Yanme'e/Drones call Palamok, with 2.2G, their home. Fittingly, all three races are quite physically strong - Elites & Brutes can match Spartans in close combat, and Drones are strong enough to lift full-grown armored human marines into the air.
 * Te, the Lekgolo/Hunter homeworld, has 4G.
 * The Lekgolo are actually small wormlike creatures that live in massive colonies, which according to the 'smaller is better' angle would be more appropriate for a high g world.
 * The Elcor of Mass Effect come from a heavy world, and as a result are very cautious and conservative in all aspects of their life, since a fall could literally kill them on their homeworld.
 * Mass Effect also has the Volus. The Volus homeworld has a high pressure atmosphere and a gravity of 1.5gs making the Volus rather short. They have to wear a pressure suit to keep their skin from splitting open when in environments that are suitable for the other council species.
 * Gravitas in Meteos is the planet in the game with the strongest gravity. Its inhabitants have little leisure time. They are about 1 meter in height and seem to be angular in shape.

Web Comics

 * Buck Godot: Zap Gun for Hire and the rest of his Hoffmanite relatives.

Web Original

 * Orion's Arm has numerous races designed and redesigned for high gravity planets. Also comes in handy on accelerating spaceships. Human tweaks adapted for high gravity are known as Anakim. They have even had their instinctive fears of falling/having an object fall on you increased, as these are much more dangerous in high gravity environments.

Western Animation

 * Tug-Mug from Thundercats.
 * An early Futurama episode involves a high-gravity planet. The only person they meet on the planet is quite short and wide and incredibly strong.

Anime & Manga

 * Zone of the Enders Dolores, i portrayed people born on Mars as being weaker than those born on Earth. It's mentioned that it's a criminal offense for an Earthling to strike a Martian, as there's a good possibility it could kill them.
 * Which is why they built themselves Humongous Mecha about six times the power of Earth models in their most mass produced forms.
 * This is also mentioned when main character James Links is challenged to a fist fight by a Martian gangster. James figures the fight will be easy as he's a Earthling, only to get his ass kicked in record time. Apparently the gangster works out in heavy G, just so he can knock arrogant Earthlings down a peg or two.
 * The Red Mars Trilogy touched on this, too - when long-time Mars residents traveled to Earth, they often needed power-enhancing suits to cope with the higher gravity.
 * Nono in Planetes. She's two meters tall. She's twelve. She was born on the Moon. However, since the human body wasn't designed for this sort of environment, the effects of lunar gravity to her physiology lead to her living permanently in a hospital, both to monitor her health as well as to aid medical research into the effects of low-gravity environments on humans—which is vital for deep-space missions like the Jupiter-bound Von Braun expedition. There is also a subversion of the "Earthborn protagonists are stronger" aspect of the trope in that professional astronauts who spend too much time in zero-G will suffer muscular atrophy and a form of osteoporosis. This is shown explicitly when the elderly Harry Roland easily overpowers the 25 year-old Hachimaki because the veteran astronaut actually made a substantial effort to maintain his muscle mass and bone density. Hachi is inspired to do the same after the incident.
 * Although the world of MAR Heaven doesn't have gravity that is notably different from Earth's, in that the humanoids look no different, it does give Ginta  an extreme power up in strength and jumping ability when compared to the standard occupants of the world.
 * Space colonies in Gundam generally don't have this issue, as they rotate to provide roughly 1G gravity on the interior. This is not as true for the Jovian colonies though, in which a full 1G of gravity is rare, and most time is spent weightless, or nearly so. A couple of Jovians in Crossbone Gundam visit the Earth and are barely able to walk across a room without collapsing.

Film

 * In Avatar, the Na'vi live on the lower-gravity Pandora. They're in the range of ten feet tall and skinny as a rail. Averts the weakness part: they're much stronger and more durable than humans, with the ability to use a hunting/war bow as tall as an average human man and their bones are practically natural carbon-fiber. Perhaps justified in that Pandora has only marginally lower gravity and the Na'vi evolved on a planet where everything tries to kill you. Not to mention that being so large, they have more places for muscles to attach too and just more muscles in general. And then the longer limbs could give them more leverage.

Literature

 * The native Martians in John Carter of Mars are considerably weaker than John Carter, who can easily make 50-foot standing leaps in Barsoom's low gravity.
 * The aristocratic Exultant caste in Gene Wolfe's Book of the New Sun are described as being very tall, possibly due to being originally from a low-gravity world and/or genetic engineering by their forefathers.
 * Charlene Dula, a visiting gamer from The Barsoom Project, grew up in the orbital colony Falling Angel. Her elongated frame reminds people of a Tolkien elf, and she has a hard time with Earth gravity despite months of intensive exercise before coming to Earth.
 * Inhabitants of Larry Niven's Integral Trees are somewhat taller and slimmer than Earth people, but they are strong, tough Heavy Worlders compared to people from the rest of the Smoke Ring. The tidal forces acting on the trees provides at least a little simulated gravity, but everyone else grows up in zero-G.
 * One character, often referred to as a "dwarf" (although it's uncertain as to whether he's actually a little person or just a throwback), has what we would call an average build, and is the only person who can wear one of the original spacesuits.
 * There's also the planet "We Made It," whose homeworld has low gravity and such severe storms that everyone is forced to live underground. Its inhabitants are all tall, wiry, and albino—basically the opposite of the Jinxians.
 * Earth's moon, Luna, is also colonized in Niven's stories. The people who grow up there, "Lunies," average around eight feet tall and are said to look like fantasy elves.
 * Martians in the Red/Green/Blue Mars trilogy by Kim Stanley Robinson. There is a section where a second generation Martian travels to Earth, but is forced to leave because the higher gravity and air pressure are damaging his health.
 * Brikar from Star Trek: New Frontier. Unusually, Brikarians aren't fragile; in fact they have some of the qualities of Heavyworlders.
 * Robert A. Heinlein's The Moon Is a Harsh Mistress uses a related idea - the tendency of muscles to atrophy in lower gravity - as a major obstacle in
 * It even goes to the point of saying that living on the Moon for more than a few weeks can cause "irreversible physiological changes," to the point that a person who has lived their whole lives on Earth will be unable to handle Earth's gravity after about six weeks in the Moon, unless they exercise regularly and "stretch time" by using centrifuges to keep their bodies adjusted to 1g. Even then, it's chancy.
 * Inverted in the Gor series, where the planet is often described as having lower gravity than Earth but the men of Gor are far stronger.
 * That's because they use the muscles they have - wind, water and muscle are Gor's only motive powers, so they get plenty of exercise. It should be noted that the occasional Earth exports - Tarl Cabot and Jason Marshall - benefit from their Earth-developed muscle mass, even though Jason takes half of Fighting Slave of Gor to find out how strong he is. Otherwise, the usual comparison is between Gorean men and Earth women, where testosterone trumps gravity every time. And though Gor's lesser gravity is, plotwise, doubtless a tip o'the hat to John Carter of Mars, Gor is much nearer to Earth in size than Mars.
 * In C.S. Lewis's Space Trilogy, the Malacandrans (Martians) are all thinner and taller than humans.
 * In The Gods Themselves Moonborn people have weaker bones, leading to slight sexual incompatibility with Earth people. And due to the metabolism being about the same, they need constant exercises to keep their bodies under the proper strain. A human from Earth who comes to the Moon must spend at least a week every two months on Earth, unless he wants the path back cut off for him.
 * The "1 on 1" gamebook Battle For The Ancient Robot had Zanleer from Venus as one of the human player's allies. His vital stats are given as 7' 6" and 169 pounds. As an aside, the surface gravity of Venus is about 90% of Earth's.
 * Sector General again, this time with the GLNO Cinrusskin, a meter-long insectile species from a planet with 1/8 G. Requires an antigravity belt to survive, much less be able to move in 1G conditions (if the belt failed it'd die of shock within minutes, assuming its exoskeleton didn't collapse first).
 * In the Green-Sky Trilogy, the titular world does have much lower gravity, so much that a toddler's fall from the high treetops will injure, but not kill. The Kindar are on the willowy and frail side, while the ground-walking Erdlings  have developed a sturdier frame from generations of living underground.
 * In the Hyperion series, Kassad is from Mars, which has a lower gravity than Earth. He's he's very tall and slender, but he keeps in shape (It helped that he had to spend a year as a menial worker in a 1.3 G environment).
 * The Martians in War of the Worlds are massive, octopus like beings who could walk on their tentacles on their home planet, but can only drag themselves on their bellies on earth.
 * Honor Harrington also features a few lightworlder characters, such as Joachim Alquezar from the Talbott Quadrant world of San Miguel. They are described as being tall and lightly built.

Live Action TV

 * Elaysians from Star Trek: Deep Space Nine and Star Trek: Titan. They are fragile.
 * Star Trek: Deep Space Nine gives a Lightworlder in Melora Pazlar, who is mostly bound to a wheelchair (or a quite clumsy "exoskeleton" harness) because of her difficulties in adapting to standard gravity. In her quarters, she turns the artificial gravity to that of her world. Dr. Bashir tries a strengthening regimen, but when told it would be irreversible (thus making it impossible for her to return to her homeworld), she declines.
 * Eventually, Melora beat some bad guys by turning off the artificial gravity and being the only one who could easily maneouver. Melora can currently be found in the Star Trek: Titan book series.

Tabletop Games

 * The Tau of Warhammer 40,000 includes the Air Caste, the Tau social class who crew the empire's spacefleet. As they have lived almost exclusively in a low-gravity environment for generations, they are described as having developed very fragile, lightly-built bodies.
 * Other Tau castes aren't much better. Your run-of-the-mill Fire Warrior barely gets to the chest of his Guard counterpart, and is so physically weak that average human can tear him apart without much effort. In short, the normal human is for a normal tau what a Space Marine is for him—and that's why Tau suck in a close combat. So, they tend to compensate for it with a lot of Beam Spam.
 * In fairness, a Fire Warrior is about as tough as a human and has about the same stamina, but lacks a human's reflexes. This is played totally straight with the other Tau castes though, as the Fire Warriors are the toughest and strongest of the Tau and they only come up to human-level, if that.

Video Games

 * In Halo The Covenant has two prominent light-worlders in its ranks. The Kig-Yar/Jackals hail from Eayn, which has 87.5% Earth's gravity. They are not physically strong or durable (being birdlike and thus likely having fragile skeletons doesn't help them either), relying on shields to protect them. However, even in Earth gravity they're pretty fast on their feet. Unggoy/Grunts come from Balaho, which has only 70.8% Earth's gravity, but are actually pretty strong judging by the weapons they've been seen carrying; in First Strike the ODST Cpl. Locklear has great difficulty hefting a fuel rod cannon over his shoulder, while Grunts carry FRGs with no problem.
 * Some of the Unggoys' strength might be due to their homeworld being a Death World, with flame geysers and other hazards. This is also responsible for their rapid rate of reproduction, to the point where contraceptive chemicals are put in their gas and food while offworld to prevent overcrowding.
 * Master of Orion has planets with low, normal or high gravity, higher ones naturally being both bigger and denser (i.e. more often mineral-rich). Races with trait "Low-G World" have 10% ground combat penalty (though compensating iit costs less points), while "High-G World" gives +1 hit point to troops. All 3 variants get a fitting homeworld and penalties to all production on planets with different gravity.
 * Vega Strike has Spaceborn (Homo Sapiens Cosmonatalis) among the Human Subspecies. Game-wise, they are a subfaction of the Andolian Protectorate. Story-wise, they were genetically engineered in secret by Lightbearers as a zero-G Servant Race, then discovered and liberated by the Andolians during the first big space war of the Humanity (which turned against Lightbearers other human factions, even their former allies). Of course, they live almost exclusively at various orbital facilities.

Webcomics

 * Inverted in The Inexplicable Adventures of Bob, where Voluptua has said she is more fragile than she looks because Earth has higher gravity than her homeworld.
 * In fact Fructose Riboflavin (same species) refers to Bob (a completely normal human) as a heavyworlder while fighting him.