med stud said:
A muscle is capable of pulling 3-4 kg/ square centimeter of cross section. That's really all it's about. Some people might be able to pull 4.5 kg/square centimeter and some people 2.5 kg but still the strength of a muscle is directly proportional to how big it is. But:
1) The size of the muscle and the size of for example an arm doesnt have to be the same thing, especially not in an obese person.
2) All instances of muscle use is improved by practising; this is most obvious in martial arts but that's true even for weight lifting. In martial arts you almost never use one muscle so a small, wiry guy with exceptional coordination can practically be very strong. But isolate the wiry guy's muscle in an exercise and you see that his strength isnt really that dramatic. For D&D purposes I would say that you are right, though.
This is sort of a semantic issue, but really, what's the more "dramatic" strength? The big burly guy who can bench press 350 lbs but can't throw a punch, or the wiry guy who benches 175 and hits like a ton of bricks. Explosiveness and sheer strength are not strictly linked, after all.
And the length and density of the muscle is just as important as its girth. For example: I'm 6'3". A friend I work out with is 5'7". Both of us have 16" biceps. Mine, however, are a few inches longer than his, due to my height. As a result of these differences, he outperforms me handily on bicep isolating exercises. In fact, he outperforms me on almost every well-isolated exercise. As an added irritant, on him these biceps look massive, and on me they look about average. My only consolation is that his advantage disappears when we start doing mixed muscle groups and my endurance is substantially greater.
Furthermore, there are substantial differences in muscle density between people, as well as muscle shape and the ratios of short and long twitch fibers. It's just about the only place where one can find statistically significant differences between racial groups. Africans tend to have denser, stronger, better shaped muscles than anyone else. There are always exceptions, of course, but generally, they don't have to work as hard for equal gains.
In any case, the strength of a muscle is related to how big it is, but there are many other factors.