That's true, but I don't think GP was referring to those special cases where the risk is to the brain, even though those are the what the linked article of cour

That's true, but I don't think GP was referring to those special cases where the risk is to the brain, even though those are the what the linked article of course discusses. As their parent comment said, any sport that compels you to reach for the extremes of physical human performance carries a risk of injury and wear that's obviously greater than just exercising for health and casual fitness. In most cases that's to something else in your body than your brain. But that reaching for the limits is also what makes those sports enjoyable to some people, and nothing else might quite equal the experience.