Downhill Mountain Biking
Evidently, riding uphill isn't much of a problem. Mountain bikers can travel up to 70 miles per hour straight down a mountainside. Roots, rocks, hikers, and other hard-to-miss obstacles could stand in their way, and they wouldn't know until it was too late. Every crash is life-threatening, or at least extremely painful.
Broken Bikes, Bones and Catching a Ride Home
Fortunately, there have only been a few deaths in the mountain biking community. However, that community is extremely small and it is assumed that 1 in 10 of all riders will suffer a serious injury at some point in their career. Please wear a helmet.