level to allow for extra strength when tightening the boots. Poles Ski poles, one in each hand, are used for balance and propulsion. Helmet Ski helmets reduce the chances of head injury while skiing. Ski helmets also help to provide warmth to the head since they incorporate an inner liner that traps warmth. Helmets are available in many styles, and typically consist of a hard plastic/resin shell with inner padding. Modern ski helmets may include many additional features such as vents, earmuffs, headphones, goggle mounts, and camera mounts. Protective gear The protective gear used in alpine skiing includes: mouth guards, shin guards, chin guards, arm guards, back protectors, pole guards, and padding. Mouth guards can reduce the effects of a concussion and protect the teeth of the athlete. Shin guards, pole guards, arm guards and chin guards are mainly used in slalom skiing in order to protect the body parts having impact with the gates. Back protectors and padding, also known as stealth, is worn for giant slalom and other speed events in order to better protect the body if an athlete were to have an accident at high speeds. Competition Elite competitive skiers participate in the FIS World Cup, the World Championships, and the Winter Olympics. Broadly speaking, competitive skiing is divided into two disciplines: Racing, comprising slalom, giant slalom, super giant slalom, combined, and downhill, parallel slalom and parallel giant slalom. Freestyle skiing, incorporating events such as moguls, aerials, halfpipe, and ski cross. Other disciplines administered by the FIS but not usually considered part of alpine are speed skiing and grass skiing. Ski trail ratings In most ski resorts, the runs are graded according to comparative difficulty so that skiers can select appropriate routes. The grading schemes around the world are related, although with significant regional variations. A beginner-rated trail at a large mountain may be more of an intermediate-rated trail on a smaller mountain. In the United States and Canada, there are four rating symbols: Easy (green circle), Intermediate (blue square), and Difficult (black diamond), and Experts Only (double black diamond) Ski trail difficulty is measured by percent slope, not degree angle. A 100% slope is a 45-degree angle. In general, beginner slopes (green circle) are between 6% and 25%. Intermediate slopes (blue square) are between 25% and 40%. Difficult slopes (black diamond) are 40% and up. Although slope gradient is the primary consideration in assigning a