I think that a great deal of injury with running (or anything else) relates to the strength of the connective tissues and the smaller muscles. Some people have a pretty good muscular system.

I have muscle in some ways. But shifts sideways can nearly trip me to the ground, strain to the hip flexors in certain positions can as well, and although I can squat to get something off the floor, doing it properly on my heels makes my knees feel so terrified I don't dare. I think this simply means that while the primary main muscles are ok, the connective tissues, ligaments, and some of the smaller less-used muscles are not up to dealing with my weight.

There's always going to be things that some people can do... a friend's wife is 330 and on crutches because she's too heavy to walk, yet I weigh 375 and I can mow the lawn and walk around for a few hours at the stores -- people are different.

But the reality is that MOST people who are severely obese are at incredibly high risk of injury from rapid and impact exercise.

And the real problem is that most people tend to leap into exercise too rapidly. And most obese people at one point were thinner and, rather like ex druggies LOL, tend to overestimate what they can handle as a result.