The study on damage caused to mountain bikers used a sample group of extreme MTbers in the Austrian Alpes who ride several hours a day.
The control group was a bunch of medical students who used bikes for commuting a few miles in a city.
The scientific result was that taking numerous crashes, and pounding downhill at high speed is not good for you, compared to normal riding around town, and can result in the buildup of scar tissue.
The result of the research according to the newspapers was that cycling is bad for you.