Snowboarding
Downhill techniques, alpine, telemark and snowboarding, all perform turns by rotating the ski or board onto its edge. Once on edge, the curved pattern cut into the side (the "sidecut") causes the ski or board to bend into a curve. As they move forward over the snow, this curved shape causes them to turn.
On skis, the foot is pointed in the direction of travel, and the rotation onto the edge occurs by moving the leg to the side. In comparison, snowboards are normally ridden "sideways", with the foot pointed across the line of travel. Rotation onto the edge requires the legs to be moved back or forward, or more exactly, by weighting the toe or heel. Whereas ski boots and bindings are very stiff laterally and relatively flexible fore and aft, the opposite is true for snowboards.
Additionally, in the case of skis the dangerous falls occur when the legs are forced away from the heading of the upper body, twisting the knee and lower leg. This can occur when the skis can move in different directions, and such accidents are common when one ski catches an unseen obstacle like a tree root. Ski bindings need to be able to release the boot in these situations, and prior to the invention of modern bindings, spiral fractures of the lower leg were common. Snowboards keep both legs pointed in the same direction at all times, and this particular form of differential twisting is not common. Injuries tend to be elsewhere on the body.
For these reasons, snowboard boots and bindings are dramatically different than ski systems. These are normally far simpler than their downhill counterparts, rarely including release systems for instance, and need to provide mechanical support only in the fore and aft directions. These typically consist of an external frame, generally L shaped, which the snowboarder steps into and then fastens down using straps over the boot. The boot itself is not as responsible for transmitting forces, and can be much softer than a typical downhill boot. When the sport was first introduced, normal winter boots were used, but today it is much more common to use semi-stiff snowboarding boots. Some specially disciplines use harder boots with step-in bindings, more similar to downhill systems, but these are not widely used outside these fields.
Read more about this topic: Ski Boot