Sorry if the question isn't clear. With understanding that zweihänders were used to destroy long-handled weapons and would wreak havoc in pike formations, would the wielder of it be wearing considerably more armor compared to his soldiers? What would the differences in armor be?
With regards to the physical requirements, were zweihänder soldiers trained differently? Were they generally bigger in stature to accommodate for the larger weapon?
The guys who wielded zwiehanders weren't armored juggernauts. At most, they wore armor similar to that worn by the front ranks of a pike formation, ie breastplate, upper leg guards, shoulder, maybe some armor on their upper arms, and some leather gloves.
To my knowledge, these weapons didn't see much use past the middle of the 16th century, and they were probably not very useful long before that. In truth, pike heads are really hard to cut off. When you strike the head of a pike, it tends to move out of the way, which lessens the blow. Pike heads were also typically connected to the pike by metal strips at least a foot long. In addition, a pike could be driven through metal armor. Pike formations like the early Tercios and swiss pikes tended to move rather rapidly which would result in the swordsman either being rapidly overwhelmed and skewered to death, or they would become useless as they would run from the pikes, and become pressed against their own soldiers and thus lose the ability to swing their swords.
Zweihanders were awkward weapons to use in battle. Their size means that the wielder needs lots of room, which leaves them open to attack by cavalry, or by advancing masses of enemy soldiers. Really they would only be useful against a static group of pikemen. Even then, it would be dangerous because you would essentially have to approach, nearly alone, against a pike force that would almost certainly be backed up by musketeers.
In my reading on 16th century warfare, the only time I've read a primary source on zwiehanders was a quote from an italian guy making fun of them. I'll see if I can find it later.
Sources:
Bert Hall "Weapons and Warfare in Renaissance Europe"
Alan Williams "The Knight and the Blast Furnace"
Just to be clear, you're asking about the differences between a Landsknecht Speißtrager vs a Landsknecht Zweihänder specifically right ?
The standard Landsknecht formation was of course the pikesquare. Consisting out of regular Speisstragers. Landsknecht veterans and frontline-volunteers would receive double-pay and thus were called "Doppelsöldner" (which means double-soldier if I'm not mistaken). Aside of the pike-frontline, Doppels would also fight in Zwehänder-formations. Having a bigger paycheck and frontline duties would obviously mean they would buy better armor for themselves. (Landsknechts in general were actually pretty well armoured beneath their faaaaabulous clothes.)
I do not believe there were specific physical requirement for the Zweihänders. A pike and a greatsword are both approx. 6 kg. So you wouldn't expect a regular LK pikeman to be physically any less impressive than a swordsman. Just maybe less armored. Wielding a greatsword does require specific training though. Fencing with a sword is less straight forward than wielding a pike. Germany had a lot of great martial arts centres so I'm guessing getting proper training was not a problem for LK-vets who volunteered for Zweihander-duty.