I think you assume way too much out of this: The way I usually hear this expression is like "I have tried to do a backflip, failed and broke my arm", or so. So

I think you assume way too much out of this: The way I usually hear this expression is like "I have tried to do a backflip, failed and broke my arm", or so. So the blog writer likely did something way out of his league, like a fancy trick, and it is not a fair assumption to think that he lives such a sedentary lifestyle that any kind of movement would cause him harm, or even thinks that way. One can be very sporty, yet do some stupid one-off movement that will cause harm.