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 tyres, 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.