The first ski for people in wheelchairs was designed in 1978 at Stanford University. The Department of Veterans Affairs Rehabilitation Research and Development Center later developed the Arroya Sit-Ski. The Arroya Sit-ski features four inward-facing stainless steel edges that allows seated skiers to traverse, turn and stop by shifting their body weight. A tunnel section between the runners reduces surface friction and increases traveling speed. Beneficial Designs, Inc. manufactured the Arroya Sit-ski from 1981 to 1985. Magic in Motion developed the popular Shadow mono-ski in the mid 1980's. It consisted of a seat mounted to a single downhill ski by a steel and aluminum frame which utilized a motorcycle shock absorber allowing the ski to pivot under the monoskier. This new type of monoski also featured a lifting system which allowed the monoskier to 'lift' the ski seat the height of the ski lift. Several years later saw the invention of the adjustable "boot" type seat to better secure the monoskier to their monoski. The early 1990's saw an explosion in monoski manufacturers and styles. The suspension style shifted from a pivot mechanism which allowed the ski to articulate under the seat while keeping the feet stationary in relation to the ski to a more advanced triangulated shock absorber system which allowed the ski to travel up and down in relation to the feet and seat of the monoskier. The triangulated system is in use on most monoskis today with a few exceptions. Many newer ski designs of today also utilize standard ski bindings instead of monoski specific ski binding plates.