I am only about 110 pounds and some unleashed dogs that come running at me while I'm out on the trails weigh almost as much as I do. Fortunately it has been a long time since one has been aggressive or menacing. Most of them are super excited and want to play or run with me. Often, they jump on me. I've been knocked down or nearly been knocked down numerous times by happy large dogs that are nearly as big as I am. One playfully jumped at me with its forelegs going right into my stomach -- it was like being punched.
Invariably, the owners say "Oh, s/he's friendly!"
Yes, well, that's obvious, but your friendly dog still hurt me. Keep it on a leash.
It also ticks me off when the owners yell at the dog for jumping on me. Hey, stupid owner. The dog is just being a dog. Control it and maybe it won't "be bad".