these people start at a young age, they are sponsered and get paid even if they are injured.
dont get me wrong im not saying im some sort of would have been, but i wouldnt even try now. if i fell off and got hurt being self employed id have no income. for them it just adds to the coolness if you break a leg or recieve a massive gash, specially if its caught on film, they have nothing to lose, having nothing to lose means you take bigger risks and get that good.
il stick to singletrack!