There's a few bits of evidence here and there that wizards are physically different to Muggles.

From the original 7 books:

Hagrid does not seem to think that a car crash could kill wizards.

Wizards get colds but can cure it.

Bludgers are large iron balls, somewhat like cannonballs. They likely move at around 100mph, because they can keep up with a Nimbus 2000 but not overtake it. So Harry is hit in the head by a cannonball moving at approx 100mph and survives. A Muggle's head would have been squashed by that.

On the other hand, Neville's wrist broke fairly normally in PS.

While we're on the topic of bludgers, the very fact that wizards can hit them with a bat and not break their arms is also of note.

From Fantastic Beasts:

You don't get much more explicit than that. Unfortunately he doesn't expand on the topic...

The use of "your", the fact that Newt isn't wearing a helmet, in combination with the earlier quote about physiology, rather implies that Jacob's skull needs much more protection than Newt's.

From Pottermore:

From Interviews:

http://www.accio-quote.org/articles/2001/0301-comicrelief-staff.htm

http://www.accio-quote.org/articles/2000/1000-scholastic-chat.htm

Of course, in DH Dumbledore's age was significantly decreased, and McGonagall's age is all over the place. Nonetheless I think it's clear that wizards live significantly longer than Muggles.

Conclusions

So, with all of this in mind, what would you say are the physical differences between wizards and Muggles?

 

To what degree would you attribute Neville's uncle's belief that he would be fine when dropped from the window to his innate resilience or was it a reliance on spontaneous accidental magic?

Oliver Wood took a bludger to the head and was fine, Ron was poisoned by dragon venom, Harry's only real injury from a bludger was a broken arm. We don't really hear much about injuries in Hogwarts, but how much of that can be laid at the feet of their inherent toughness vs. how easily they can correct mundane injuries is up in the air.

 

TL;DR Harry is a pussy for spending so much time in the Hospital Wing. The other kids just walked it off.

 

I love this. New headcanon.

 

What if the magical equivalent of vaccines are basically protective enchantments that the neo-natal Healers at Saint Mungo's can apply to children? Someone like Hermione would have been caught up as soon as she went to school.
Alternatively, magic may come out involuntarily, the same way as breathing. Innate physical resistance seems like a genetic matter, and that would require theoretical blood purist explanations of magical children with muggle parents(infidelity, adoption, etc) to actually be the case.

 

The Pottemore article about werewolves explains that Wizards are less likely to bleed to death from a werewolf attack and are thus more likely to be turned, so it seems that bleeding is less severe for wizards than for muggles.

About Reproduction something special we know is that James Potters mother was considered elderly even for wizards when she had James, Pottmore mentions that it was suprising, but the way its mentioned the suprising part is considering the long time she and her husband were unable to have children. So we know that its at least possible for witches to have children in their 80s-100s without the aid of magic.

 

"I borrowed this from Perkins at the office. Doesn't camp much anymore, poor fellow, he's got lumbago." - GoF

Not earth shattering but something that is inconsistent with the general principle of wizards being tougher.

 

Could be that a Wizard's survival instinct acts through their magic to provide a passive protective effect. This effect might be stronger in proportion to the danger, which would explain why a bludger can break a wizard's arm but not splatter their brains all over the spectator's faces. Their aging process somewhat match this as well, it seems that a wizard ages normally until their sixties or so, only when aging starts to become life threatening does it starts to slow down.

 

Like a magical adrenaline? I like it.

 

We don't know how old Perkins is, or what caused his lumbago. If he's 150, and has lumbago because he spent 50 years having bludgers slam into his back at a 100mph or because of an unfortunate incident with a set of cursed bowling balls (perhaps more likely given his line o work)...I think thats reasonable. If he's 45 and has lumbago because of spending too many years hunched over a desk...not so much.

Personally I like the idea that the magic at work is instinctual, much like accidental magic. Its targeted by survival instinct and nothing more, as @Heosphoros puts it that is why arms get broken but not skulls.

 

I personally go with them having cartoon-physics durability that scales with their power. Children are an exception as they can make up for their lack of power with accidental magic.

Since it's based on cartoon-physics, it's not very reliable. In any situation a wizard should prefer to actively cast magic to protect themselves instead of hoping their constitution will protect them.