Short answers, pulled from the story.
Mountain biking, abbreviated MTB, is the sport of riding bicycles off-road over rough terrain using specially designed mountain bikes. These bikes use features such as air or coil-sprung suspension, larger wider wheels and tires, stronger frames, and disc brakes to improve durability and performance off-road.
The sport originated in California on Marin County's Mount Tamalpais, where riders modified heavy cruiser bikes for off-road use from the late 1960s to the late 1970s. The first organized downhill series, the Repack Races, took place in Fairfax, California.
Joe Breeze is normally credited with introducing the first purpose-built mountain bike in 1978. Tom Ritchey built the first regularly available mountain bike frame, which Gary Fisher and Charlie Kelly accessorized and sold through their company, MountainBikes.
The first two mass-produced mountain bikes were the Specialized Stumpjumper and the Univega Alpina Pro, sold in the early 1980s. The Specialized model was first marketed in 1981 and used TIG welding to suit mass production.
Mountain biking breaks down into cross country, trail, all mountain, enduro, downhill, and freeride, along with related forms such as four-cross and dual slalom, dirt jumping, trials, and urban or street riding. Cross-country is the only mountain biking discipline in the Summer Olympic Games.
Because injury risk is determined by kinetic energy, which increases with the square of speed, each doubling of speed can quadruple injury risk. Tripling the speed brings a nine-fold increase and quadrupling it a sixteen-fold increase, and higher speed also leaves less distance to react.
The International Mountain Bicycling Association, or IMBA, is a non-profit advocacy group formed in 1988 when five California mountain bike clubs joined to fight widespread trail closures. It now represents more than 700 affiliated mountain biking groups worldwide and promotes its Rules of the Trail.