Dwarves, Elves, or Humans?
 

Which race is generally considered physically stronger?

I know this isn't really an answer, but it depends.

Having done my share of manual labor, it takes a certain kind of strength to do things like shovel or swing an axe (or a pickaxe) all day. Having also practiced boxing, wrestling, and kickboxing, it takes a specific mix of strength and stamina to produce sustained high output, or move heavy weights. It takes yet another mix, of endurance and stamina, to trek on foot all day (see: persistence hunting).

While any of the races can have members who can do any of the three, I would say that Tolkien painted a respective picture of, respectively, dwarves, men, and (wood) elves.

Edit: I hope that was clear. I'm finishing up some honeyed mead and on my way to bed. :-)

I would think the Dwarves due to all the physical labour they do with stones and metals and they certainly are a tough people. Elves have the greatest control over their bodies and can take a lot of physical punishment.

Dwarves seem to be strongest. Tolkien made a point (in The Silmarillion?) of noting their toughness and endurance. On the other hand humans seem best at, ah, getting lots of new humans so as to outnumber the others.

I have to agree with you, Tuor.
Since Aule created his Children when Melkor was having dominion over Middle-Earth, he made them physically strong so that they could endure his evils, as well as fast in both friendship and enmity. Moreover, it is stated that Galadriel, one of the most important Elves of the Second and Third Ages, viewed the Dwarves as a general and saw in them the best fighters against the Orcs.
King Naugladur.

This doesn't really prove anything, but Professor Tolkien does state in "Of Dwarves and Men" that Dwarves were "the most redoubtable warriors of all the Speaking Peoples" which suggests to me that they were naturally or typically the most formidable in general.

That being said, it reminds me of our topic about the Balrog - I suspect that there were heroic individuals among Men and Elves that were probably as strong as if not stronger than the average Dwarf, whereas the Dwarves produced less individually heroic characters. The point of Dáin Ironfoot seems to be to provide a noteworthy exception to this.