How much of an advantage in medieval-style combat would it be to have four arms with pivoting shoulders?

Question

So I'm writing a story about humans of the modern world being given various superhuman powers by an unknown entity, which eventually causes society to partially collapse and turn into a bizarre mash-up of post-semi-apocalypse and sword and sorcery adventure (various omnipresent powers render most of modern technology useless in a fight, causing people to fight exclusively with medieval-grade weapons and their various superhuman powers).

Now, one of the various things to result from this is the introduction of fantasy races into the world via giving humans the power to shapeshift, and one of the features I knew I wanted to add to one of the fantasy races in my story was an extra set of arms, since the possibilities that opens up both in combat and in everyday life are fascinating to me. But it occurred to me that most of the places an extra set of arms is usually placed on such races would probably run a serious risk of the arms getting tangled up or bumping into each other. So I spent a while trying to find a way to integrate an extra set of arms in a way that would sound right when described and actually work well in practice.

The idea that resulted is essentially that the four arms would all be mounted on the traditional human shoulder area (with a thicker upper torso to let them fit both shoulder joints side by side), but with more flexible shoulder joints for each and a special, additional, internal shoulder joint that, by a combination of weird biology and straight-up magic, allows them to actually rotate the relative orientation of these shoulder joints to each other so they can shift the positioning of them from back-to-front to up-to-down and even a little further upward, so that they can alter the most practical positioning of the arms for what they want to do and, more notably, if they use both arms on one side to grab a single object, they can swing that object around with two arms as if it was one arm and have the same range of movement that a human would have swinging around one arm. Each arm would have the strength of a human arm, and the internal pivoting shoulder joint would have the 1.5 times the strength of a normal human shoulder joint (keep in mind that most of the characters in this story have their strength further doubled by an omnipresent power as well).

Now to me this sounds like a huge advantage. Even realizing the practical limitations on wielding multiple weapons at once, being able to have 50% to 100% more force behind a blow, carry multiple shields, wield a two-handed weapon with a slight sacrifice to grip strength and still have two more hands, wield a bow and arrow while riding a bike in a world where cars are useless and horses are scarce, and utterly dominate hand-to-hand combat with terrifying grappling techniques and hybrid offensive-defensive stances (keep in mind that bare-fisted combat is much more practical here as everyone's hands, feet, head and neck are all but indestructible) sounds like the advantage they'd have over a normal human would be ridiculous.

In fact it seemed like such a huge advantage that when working out how to balance this race, I concluded that merely having their physiology, their arms combined with their generally slightly stronger and more durable bodies, would have to be balanced by severely reducing the types of magic powers they have access to (to keep humans from becoming the boring jack-of-all-trades race, humans are the only ones who can use all six types of magical abilities in my story, and each race pays for their advantages over humans by losing access to at least some of them, usually just one type). I realize it would be impossible to briefly summarize my design philosophy of the powers, so let's ignore them for now and just assume for the sake of argument that they're designed such that mages and physical fighters are pretty much balanced, all other things being equal, and that fighters have the same number of powers as mages, just generally in more physical abilities.

Am I correct in thinking this would be a huge advantage in combat with medieval-level weaponry and that they'd need to pay a steep price elsewhere to be balanced? Am I overestimating how useful this would be? Am I underestimating it? Or is there some fatal flaw I'm missing with the arm setup I've described that I need to work out?

Answer 1

Your shoulder knights would make very effective shield walls and phalanxes. Each soldier can carry two shields and two spears in some combination of overhand and underhand. Overhand is better for not hitting your friends with the butt of your spear. So your force has twice the covering per person and presents twice as many points to the enemy. With proper drilling the extra arms shouldn't get in the way if they restrict entirely to thrusts.

Another possibility is one shield, one or two rondel type daggers and two free arms for grappling. This unit would be a specialised at countering heavy armor. The idea is to close quickly, block the first blow, then grapple and opponent and stab through the neck/visor/armpits. Again sticking to the thrust there is less problem of the arms interfering with each other.

In all other forms of combat I see the extra arms getting in the way of each other. Four swords is certainly a bad idea since historically two weapons was just a substitute for one weapon and a shield.

For personal combat I see the shoulder-knights sticking mostly to two-arm style -- already superior to a human fighter -- but with the opportunity to decouple the inner arms and grab their opponents' arms if the opportunity presents itself.

Using two long weapons is probably out. But one advantage of four arms is the wider grip it offers on a weapon. So you might see a three arm style with a heavy shield and a long weapon like a halberd gripped about three feet apart with both right arms. Then you have the purchase to deliver the sort of swings a human has to ditch the shield to achieve. Still this is more for personal combat and wouldn't work in dense formation without chopping your friends' heads off.

Problem: This is your world, so maybe it is common to carry around large weapons for personal defense? But historically I think it was uncommon to carry around battlefield sized weapons unless you were on the battlefield and ready for mass combat. So there was no cause for a large weapon that is effective in duels but ineffective on the battlefield.

Answer 2

There's a significant advantage to holding a sword with two hands, and your four-arms guys could do that and still hold a shield (or two shields).

The advantage of holding a sword with two hands instead of one is leverage, which gives much greater strength and control. It either allows wielding a longer and heavier sword with the same strength and control as a shorter one in one hand, or allows wielding a more normal-sized sword with more quick movements and better leverage than one-handed.

Your four-arms guys have all the advantages of a two-handed swordsman but not the main disadvantage: the lack of a shield.

So oddly enough I think your four-armed men would do very well going into battle with a single large sword or mace held with both the arms of one side, and a shield or shields on the other side. Although you'd think using the conventional setup would be a waste of their unique traits, that wouldn't be the case at all. They'd wield the sword and shield with much greater strength and agility than other men. They'd be extremely hard to face by a man with two arms. When going up against a two-handed swordsman, you can't sword-fight with them, because their sword blows are just much stronger than yours. You try to catch their sword on your shield and then stab when they're exposed (because they have no shield). But your quad-arms have that same two-handed sword advantage...and also a shield.

An even deadlier setup might be a greatsword in the two right arms, a shield in one left arm, and a light stabbing sword in the other left arm. Swing the greatsword, they get knocked hard, but catch on shield, they thrust with their sword, you deflect with your shield, and finish them with the stabbing weapon you had tucked behind the shield.

Answer 3

I fully agree that these dudes would be a wrestler’s worst nightmare, to the point where grappling might the dominant strategy for this group. What you could is to say they have some issues with coordination, not because their arms get tangled, but because they have so many limbs to work with and balance. Learning combat skills could take longer for this species (race?), so humans and other peoples could be better combatants on average. Once a Shoulder-lord gets good, though, it can utterly dominate. Until then, they could have a real problem with overconfidence.

"My uncle Linny took on four humans at once. I can take one."

"Your uncle Linny practiced two hours every day for five years, Chuck. You're going to accidentally cut your own hand off half way through the battle, assuming you don't just fall over when you overbalance and get stabbed through the back."

Other than that, this race doesn't have that big of an advantage at ranged warfare, which other magically gifted species could exploit. If you keep the shoulder-lords at a distance, people can take them out with arrows, fireballs, and any other ranged attacks you can think of. Shields would be a good counter, but shields aren't perfect.

Because these dudes are top heavy, would they have slower movement speeds?