Mountain biking is a sport of riding bicycles off-road, often over rough terrain, usually using specially designed mountain bikes. Mountain bikes share similarities with other bikes but incorporate features designed to enhance durability and performance in rough terrain, such as air or coil-sprung shocks used as suspension, larger and wider wheels and tires, stronger frame materials, and mechanically or hydraulically actuated disc brakes. Mountain biking can generally be broken down into five distinct categories: cross country, trail riding, all mountain (also referred to as "Enduro"), downhill, and freeride.This sport requires endurance, core strength and balance, bike handling skills, and self-reliance. Advanced riders pursue both steep technical descents and high incline climbs. In the case of freeride, downhill, and dirt jumping, aerial maneuvers are performed off both natural features and specially constructed jumps and ramps.Mountain bikers ride on off-road trails such as singletrack, back-country roads, wider bike park trails, fire roads, and some advanced trails are designed with jumps, berms, and drop-offs to add excitement to the trail. Riders with enduro and downhill bikes will often visit ski resorts that stay open in the summer to ride downhill-specific trails, using the ski lifts to return to the top with their bikes. Because riders are often far from civilization, there is a strong element of self-reliance in the sport. Riders learn to repair broken bikes and flat tires to avoid being stranded. Many riders carry a backpack, including water, food, tools for trailside repairs, and a first aid kit in case of injury. Group rides are common, especially on longer treks. Mountain bike orienteering adds the skill of map navigation to mountain biking.