It is 6 occurences per 100000 people in base population, but much higher among people who do CrossFit. That was exactly the point of the article:
The claim that rhabdomyolsis is more frequent in CrossFitters is the question you and Nancy appear to be begging. We have nothing other than anecdotal evidence to support that.
I think it is rather self evident that injuries that result from over-exertion will tend to result at a higher frequency during activities with high levels of exertion.
The criticism seems to be from people who are unfamiliar with the pursuit of high level athletic goals. Injury is a possibility when you set out to reach unprecedented heights of physical fitness. If you want to burn some calories and avoid any potential problems, walk the dog. If you want to accomplish what these Crossfitters do, then there are risks.
Edit to add: I should say that I actually agree with Nancy's original point that we should "evaluate our competitions carefully". I think you should decide what you are trying to achieve and consider the risks inherent in that pursuit. CrossFit is only an example of one kind of relatively extreme training. It is trying to approach the limits of what is physically possible, and that involves risk.
We have nothing other than anecdotal evidence to support that.
For extremely rare events, even anecdotal evidence can be pretty good. If you were told something happened to 1 in a billion people, and you met 3 such people, you'd have pretty good evidence that something odd is going on (the rate is a lie, you're mistaken about meeting them, or something unusual is concentrating them in your presence). Rhabdo isn't nearly that rare, but it's pretty rare. That rareness, and a very reliable base rate for rhabdo in the overall population, means that the anec...
Here's an internal dialogue I just had.
Q: How do we test rationality skills?
A: We haven't come up with a comprehensive test yet.
Q: Maybe we can test some part of rationality?
A: Sure. For example, you could test resistance to akrasia by making two contestants do some simple chores every day. The one who fails first, loses.
Q: That seems like a pointless competition. If I'm feeling competitive, why would I ever skip the chores and lose?
A: Whoa, wait. If competitiveness can cure akrasia, that's pretty cool!
Now we just need to figure out how to make people more competitive in the areas they care about...