Superheroes. Most of it related to modeling strength.
Rather than post some big-ass essay, I'll give you some highlights. Here's a real life individual who's a good example of a person with a (B/X style) strength of 18:
|He's smiling at your puny muscles.|
For a B/X-based game, where a strength of 13+ indicates a damage bonus, I think it's fair to consider that bonus based on training, explosive speed, and the ability to add extra injury with the occasional mixed-in, non-weapon blow (an elbow, kick, shield-bash, etc.). A lot of stuff can happen in a ten second round, you know?
But that actually has little to do with the superhero game (because the system is different from "straight B/X")...it's just the precursor that led me to the line of thought for my super heroic strength modeling.
See, most superhero RPGs have some way to model "super strength" (a staple of comic book super powers, since, oh Superman; i.e. a long-ass time), and the usual route is to do some sort of quantitative method in a ranking system. For example, the original Marvel Superheroes did the RM, IN, AM, MN, UN, etc. ranks that measured superhuman strength in terms of tonnage (1, 10, 50, 75, 100, respectively). Aberrant had a one-five point "mega-attribute" system (also in tons: 1, 10, 25, 50, 100). Supers! does the same thing with dice (the more dice, the more tonnage), while Heroes Unlimited categorizes strength into four different tiers (normal, exceptional, superhuman, and supernatural) with each tier determining the exact amount that can be moved based on the character's Physical Strength attribute (exceptionally granular, in a way that makes Mutants & Masterminds look almost abstract).
But I'm not going that route. You see, I figured something out: when it comes to lifting heavy objects, strength, for most individuals (comic books individuals) is mainly tied to one's physical mass. After training, of course.
Look at the weights that are lifted by Olympic weight lifters. Male or female, you can see that the limits of what can be snatched, cleaned, and jerked is limited to a bit more than twice a person's physical mass...and there's a rate of diminishing returns for adding more muscle. A larger human has the potential to lift a larger amount of weight, but the overall percentage becomes smaller the bigger the human. The world record for a clean and jerk lift for a 53kg woman is 134kg: 253% of her body mass. The record for a 105kg man is 246kg...only 234% of his body mass. By the way, these kinds of numbers hold true for power-lifting MMA fighters who are as much concerned with speed and stamina (if not more so) than with physical power.
Of course, we're talking about people who power lift as a profession. Most of us don't. Most of us don't have 18 strength either. But we can still get an idea of peoples' ability to lift and carry. I find several references to minimum body weight requirements of 150 pounds for firefighters. Full kit for a firefighter (who is presumably in good condition) is a bit more than 70 pounds...half their weight (which they're required to lug up and down flights of stairs in rather perilous situations). So using our abstract B/X strength (STR) ladder, I've come up with the following range of measurements:
Avg. STR/Fitness (9-12) Carry/Throw 25% of body mass
Good STR/Fitness (13-15) Carry/Throw 50% of body mass
Excellent STR/Fitness (16-17) Carry/Throw 75% of mass
Peak STR/Fitness (18) Carry/Throw 100% of body mass
Oh, yeah...there's also an "Awesome" strength category for individuals of obviously non-human proportion...dudes like the Thing or members of the Hulk family. They go up to 125% but their overall body mass is doubled, which increases their weight.
For benching, or just lifting one's maximum weight, those numbers are doubled but a good dice roll will allow you to pick up a little more (helping folks meet those Olympic level numbers).
Anyway, that's the basic calculation for "heavy lifting" based on one's fitness level and mass. Now, if your character has "super strength" as a power you simply multiply your lift capacity by 100. That's it, end of story. You're a hundred times stronger than a normal person of your mass and fitness level if you possess superhuman strength.
Surprisingly, it models fairly well for most comic book characters. Spider-Man's official weight is 167 pounds, which gives him a lift/bench press of 12.5 tons with an excellent (16-17) strength/fitness level. Luke Cage with his dense bone structure and the same fitness level as Spidey is listed at 450 pounds giving him a 34 ton range, also very close to his comic book strength level. Thing has a listed weight of 500 pounds (he has a rocky flesh, but he's not solid rock...he bleeds) a 62.5 ton range. Meanwhile, the savage She-Hulk with her 650 pound frame could lift 48.8 tons when she was "excellent" (16-17) and and 65 tons after improving to "peak" (18) with a lot of work-outs on the Fantastic Four's Thing-based exercise equipment. This models well on the old Marvel character (who had an Amazing 50 strength that then increased to the Monstrous 75 range).
Little old Captain America only weighs 220 pounds so would have a 440 pound maximum, which seems a bit low considering the world records in the category. But the guy who set a record in bench press at 440 pounds was a professional strongman named Doug Hepburn who weighed 300 pounds at the time...I think this is just a matter of Steve Rogers getting the most out of his (smaller) frame.
It's not perfect. Mighty Thor, even at a listed weight of 640 pounds, tops out a little low, and Marvel's Hercules, listed at only 325 pounds, is only about a third as strong as he should be. Oh, yeah...DC's heavy hitters like Superman (225 pounds) and Wonder Woman (165 pounds) are about one-tenth or one-twentieth as strong, but I'm working on some workarounds for the truly titanic champions of the comic book world.
Anyhoo...that's what I've been working on lately.