Isaac Asimov wrote an excellent essay some decades ago about the size of living creatures which never left me. The thrust of the essay was this:
When things increase arithmetically in size (double, treble, quadruple and so on) they increase geometrically in volume. What that means is that if we start with a creature which is five inches tall, and we increase it in every dimension by double, making it ten inches tall, the newly enlarged creature will be eight times the weight of the original.
This is the reason there are no insects or crustaceans living on land which are more than six inches in length—and those that are that long are narrow, with lots of joints. Insects have an exoskeleton, an outside plating which the meat within the body must be attached to; massive insects have a much greater meat-to-exoskeleton ratio...and after a certain point, the exoskeleton simply cannot sustain the size of the insect against the earth’s gravity.
Crustaceans also have an exoskeleton; but it is aided by the fact that most crustaceans larger than a few inches across spend all of their adult lives under water, where the water can support their weight and not the exoskeleton. Even so, crustaceans have a size limit.
Human beings and all vertabrata have an “endo-skeleton,” meaning one that is built from inside. Rather than hanging our flesh from an outer shell, our systems hang our flesh from an inner framework of bones, tendons and cartilage. This skeleton also has a practical limitation. The larger the animal, the heavier and thicker the bones must be which support the animal as it moves over ground. The lithe, graceful movements of human beings could never be managed by a hill giant, twice its size. A hill giant, attempting to do a dismount from the uneven bars (assuming the uneven bars could be flexible and still able to support the weight of the giant) would smash both his ankles as he landed.
Most of the movement in D&D which is attributed to large creatures is flatly impossible. For an example, take this: if you are ever in a jeep being chased by a tyrannosaurus, stop. Hit the brakes, then jump the vehicle three feet to the left. The tyrannosaurus, weighing around 30 tons, will simply keep right on going. It simply could not stop. If it were able to turn its head to look at you—and its far more likely that it could not—it would unbalance itself, turn ass over teakettle and then flop several times over quite a lot of landscape, ending its tumble with a broken back and well on its way to an excruciating death. The tyrannosaurus is not designed to catch small, mobile creatures which would be unable to meet its energy requirements anyway. It needs to catch very large, meaty, dumb creatures like itself which are also unable to stop once momentum is built.
In short, for most massive creatures, the concept of battle involving pivots, counter-thrusts, lunges and retreats are simply fairy-tale in concept. Which is fine. I am more than good with hill giants able to do gymnastics, as long as it contributes to the overall dramatic of the game.
Which is why I am ever astounded that a hill giant, according to the monster manual, runs at the same speed as an ordinary human being. This seems to support the argument that large creatures must necessarily move slower than small creatures because of their bulk; an argument which I’ve just made and which, I think we can agree, gets in the way of the actual playability of the game.
It has always been obvious that the original speeds of all the creatures in the books amounted to little more than random dart throwing. Why are leopards, minotaurs, swimming nymphs, owlbears, shadows and fire elementals all judged to be moving at the same speed has men? And what exactly is the logic of the original estimate for how far this distance is?
The original rule, as I remember it, was that a 12” move indicated the number of feet that a creature could move underground in the space of a minute (round), and the number of yards a creature could move above ground. I could never understand why my ability to move was suddenly cut by one third simply because I was below ground surface. Because its black? Because there are corners? Arguably I should be able to run to the edge of a well lit chamber at the same pace as the outdoors, and in a straight line too.
In any event, 120 yards a minute is the startling rate of 2 yards a second; meaning that a 100-yard-dash should take me some 50 seconds to run, roughly the same time it takes for a well-trained college athlete to run the 400 meters. I myself, at 17, ran the 400 meters in a 1:03, and I wasn’t a serious athlete. At present, in my crippled condition, I’m sure I could manage a hundred yards in not much more than a minute...keeping in mind that I am on crutches and my surgery was only four days ago.
For a game based on combat, where in hell was Gygax’s brain while he was working this out? In Cuba for the weekend? Even the OD&D fanatics must have come up with something better on their own by now...for my group, we shortened the combat round to six seconds, did a few tests with fifty pound packs and settled on a base rate of 25’/6 seconds as the speed one could be expected to sustain in combat while completely unencumbered. Oh, that’s outdoors and in.
Even that doesn’t account for running. It works out to a mile every 21 minutes, which is still slow: but we long ago worked out a method for which by the second round, you could double your speed, triple it in the third round and quadruple it in the fourth...with rules for slowing down quite similar to 3rd edition. That would mean that your top speed, unencumbered, would allow you to run a mile in just over 5 minutes...not bad, since you’re an unhealthy, medically unfit individual living in the 17th century.
How many miles could you run before you had to quit? Well, it’s never come up. I’m sure something like 1 mile per constitution point above 8 might be a place to start, with checks for stupidity after you’d managed ten miles (all long distance runners are fundamentally stupid—I was when I did that).
The point is, once we dispense with all the inconveniences of physics and its limitations on the sizes of creatures, assuming that some special magical field enables tendons to be stronger and such, we must argue that a hill giant, being twice as tall, can run twice as fast as a human, right?
I’m prepared to say yes, but with a stipulation. While I’ll go so far as to say tendons can be made stronger by the influence of bizarre magical DNA, I’m not ready yet to argue that the laws governing momentum can be tossed out of a window. Ultimately, the giant can run twice as fast: but it should take him longer to build up speed from a position of rest and longer to reduce speed once he’s attained maximum. Which creates a problem. Does the giant require 4 rounds to reach maximum run, or 32 rounds (8 x 4 for a normal creature)?
Oh, fuck it. It’s a fantasy game. Let’s just admit that all the creatures in the monster manual need to have their speed adjusted...in almost every case, upwards!