Fit walking is the act of walking with a speed at the upper end of the natural range for the walking gait, typically 7 to 9 km/h (4.5 to 5.5 mph), and is a non-competitive sport. Both feet can rise from the ground at any time, in contrast to power walking. Walking is one of the main gaits of locomotion among legged animals, and is typically slower than running and other gaits. Walking is defined by an 'inverted pendulum' gait in which the body vaults over the stiff limb or limbs with each step. This applies regardless of the number of limbs - evenarthropods, with six, eight or more limbs, and walk. The word walk is descended from the Old English wealcan "to roll". In humans and other bipeds, walking is generally distinguished fromrunning in that only one foot at a time leaves contact with the ground and there is a period of double-support. The most effective method to distinguish walking from running is to measure the height of a person's centre of massusing motion capture or a force plate at midstance. During walking, the centre of mass reaches a maximum height at midstance, while during running, it is then at a minimum. Regular, brisk exercise of any kind can improve confidence, stamina, energy, weight control and life expectancy and reduce stress. It also wards off heart disease, brings up the heart rate, lowers blood pressure and strengthens the heart. A California State University, Long Beach, study showed that the more steps people took during the day, the better their moods were. Why? Walking releases natural painkilling endorphins to the body – one of the emotional benefits of exercise. A brisk 30-minute walk burns 200 calories. Over time, calories burned can lead to pounds dropped. Walking does much more than work the area underneath your neck. It also has extensive cognitive benefits, improving memory in seniors, cognitive control and academic performance in preadolescents, and boosting creativity in the young and healthy. Scrambling is a method of ascending a hill or mountain that involves using both hands, because of the steepness of the terrain. Some scrambling takes place on narrow exposed ridges where more attention to balance will be required than in normal walking. Nordic walking is a physical activity and a sport, which is performed with specially designed walking poles similar to ski poles. Compared to regular walking, Nordic walking involves applying force to the poles with each stride. Nordic walkers use more of their entire body and receive fitness building stimulation not present in normal walking for the chest, lats, triceps, biceps, shoulder, abdominals, spinal and other core muscles that may result in significant increases in heart rate at a given pace. Many people enjoy walking as a recreation in the mainly urban modern world, and it is one of the best forms of exercise. There are a variety of different kinds of walking, including bushwalking, racewalking, beach walking, hillwalking, volksmarching, Nordic walking, trekking and hiking. Some people prefer to walk indoors on a treadmill, or in a gym, and fitness walkers and others may use a pedometer to count their steps. Race walking is the competitive version of fit walking, and is present at the Olympics, with three different events: 50 km men, 20 km women and 20 km men.